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Sunblock is a lotion
Lotion
A lotion is a low- to medium-viscosity, topical preparation intended for application to unbroken skin. By contrast, creams and gels have higher viscosity.Lotions are usually applied to external skin with bare hands, a clean cloth, cotton wool or gauze...

, spray, gel or other topical
Topical
In medicine, a topical medication is applied to body surfaces such as the skin or mucous membranes such as the vagina, anus, throat, eyes and ears.Many topical medications are epicutaneous, meaning that they are applied directly to the skin...

 product that absorbs or reflects some of the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 (UV) radiation on the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

 exposed to sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

 and thus helps protect against sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

. Skin lightening products
Skin whitening
Skin whitening, skin lightening and skin bleaching refers to the practice of using chemical substances in an attempt to lighten skin tone or provide an even skin complexion by lessening the concentration of melanin...

 have sunscreen to protect lightened skin because light skin is more susceptible to sun damage than darker skin, a number of sunscreens have tanning power to help the skin to darken or tan.

Sunscreens contain one or more of the following ingredients:
  • Organic chemical
    Organic chemistry
    Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

     compounds that absorb ultraviolet light.
  • Inorganic particulates
    Particulates
    Particulates – also known as particulate matter , suspended particulate matter , fine particles, and soot – are tiny subdivisions of solid matter suspended in a gas or liquid. In contrast, aerosol refers to particles and/or liquid droplets and the gas together. Sources of particulate matter can be...

     that reflect, scatter, and absorb UV light (such as titanium dioxide
    Titanium dioxide
    Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

    , zinc oxide
    Zinc oxide
    Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

    , or a combination of both).
  • Organic particulates that mostly absorb light like organic chemical compounds, but contain multiple chromophores, may reflect and scatter a fraction of light like inorganic particulates, and behave differently in formulations than organic chemical compounds. An example is Tinosorb M
    Bisoctrizole
    Bisoctrizole is a benzotriazole-based organic compound that is added to sunscreens to absorb UV rays....

    . Since the UV-attenuating efficacy depends strongly on particle size, the material is micronised to particle sizes below 200 nm. The mode of action of this photostable filter system is governed to about 90% by absorption and 10% by scattering of UV light.


Depending on the mode of action sunscreens can be classified into physical sunscreens (i.e. those which reflect the sunlight) or chemical sunscreens (i.e. those which absorb the UV light).

Medical organizations such as the American Cancer Society
American Cancer Society
The American Cancer Society is the "nationwide community-based voluntary health organization" dedicated, in their own words, "to eliminating cancer as a major health problem by preventing cancer, saving lives, and diminishing suffering from cancer, through research, education, advocacy, and...

 recommend the use of sunscreen because it prevents the squamous cell carcinoma
Squamous cell carcinoma
Squamous cell carcinoma , occasionally rendered as "squamous-cell carcinoma", is a histologically distinct form of cancer. It arises from the uncontrolled multiplication of malignant cells deriving from epithelium, or showing particular cytological or tissue architectural characteristics of...

 and the basal cell carcinoma
Basal cell carcinoma
Basal-cell carcinoma is the most common type of skin cancer. It rarely metastasizes or kills. However, because it can cause significant destruction and disfigurement by invading surrounding tissues, it is still considered malignant. Statistically, approximately 3 out of 10 Caucasians may develop a...

. However, the use of sunscreens is controversial for various reasons. Many sunscreens do not block UVA radiation, which does not cause sunburn but can increase the rate of melanoma
Melanoma
Melanoma is a malignant tumor of melanocytes. Melanocytes are cells that produce the dark pigment, melanin, which is responsible for the color of skin. They predominantly occur in skin, but are also found in other parts of the body, including the bowel and the eye...

, another kind of skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...

, and photodermatitis
Photodermatitis
Photodermatitis, sometimes referred to as "sun poisoning" or photoallergy is a form of allergic contact dermatitis in which the allergen must be activated by light to sensitize the allergic response, and to cause a rash or other systemic effects on subsequent exposure...

, so people using sunscreens may be exposed to a high UVA levels without realizing it.

Dosage



The dose used in FDA
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 sunscreen testing is 2.2 mg/cm² of exposed skin. Provided one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist, that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz) evenly to the uncovered body area. Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face. Larger individuals should scale these quantities accordingly.

Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, some research has shown that the best protection is achieved by application 15–30 minutes before exposure, followed by one reapplication 15–30 minutes after the sun exposure begins. Further reapplication is only necessary after activities such as swimming, sweating, or rubbing/wiping.

However, more recent research at the University of California, Riverside
University of California, Riverside
The University of California, Riverside, commonly known as UCR or UC Riverside, is a public research university and one of the ten general campuses of the University of California system. UCR is consistently ranked as one of the most ethnically and economically diverse universities in the United...

, indicates that sunscreen needs to be reapplied within 2 hours in order to remain effective. Not reapplying could even cause more cell damage than not using sunscreen at all, due to the release of extra free radicals
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 from those sunscreen chemicals which were absorbed into the skin. Some studies have shown that people commonly apply only 1/2 to 1/4 of the amount recommended to achieve the rated sun protection factor (SPF), and in consequence the effective SPF should be downgraded to a square or 4th root of the advertised value.A later study found a significant exponential relation between SPF and the amount of sunscreen applied and the results are closer to the linearity than expected by theory.

History


The first effective sunscreen may have been developed by chemist Franz Greiter in 1938. The product, called Gletscher Crème (Glacier Cream), subsequently became the basis for the company Piz Buin
Piz Buin
Piz Buin is a mountain in the Silvretta range of the Alps on the border between Austria and Switzerland. It forms the border between the Swiss canton of Graubünden and the Austrian state of Vorarlberg and is the highest peak in Vorarlberg....

 (named in honor of the place Greiter allegedly obtained the sunburn that inspired his concoction), which is still today a marketer of sunscreen products. It has been estimated that Gletscher Crème had a sun protection factor of 2.

The first widely used sunscreen was produced by Benjamin Green, an airman and later a pharmacist
Pharmacist
Pharmacists are allied health professionals who practice in pharmacy, the field of health sciences focusing on safe and effective medication use...

, in 1944. The product, Red Vet Pet (for red veterinary petrolatum), had limited effectiveness, working as a physical blocker of ultraviolet radiation. It was a disagreeable red, sticky substance similar to petroleum jelly. This product was developed during the height of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, when it was likely that the hazards of sun overexposure were becoming apparent to soldiers in the Pacific and to their families at home. Sales of this product boomed when Coppertone acquired the patent and marketed the substance under the Coppertone girl
Coppertone girl
Coppertone is the brand name for an American sunscreen, owned by Merck, formerly Schering-Plough. Coppertone is the sister brand to Bain de Soleil, which is targeted to adult females....

 and Bain de Soleil
Bain de Soleil
Bain de Soleil is a brand of sunscreen produced by Merck, formerly Schering-Plough Consumer Health Care. It is affiliated with the Coppertone brand...

 branding in the early 1950s.

Franz Greiter is credited with introducing the concept of sun protection factor (SPF) in 1962, which has become a worldwide standard for measuring the effectiveness of sunscreen when applied at an even rate of 2 milligrams per square centimeter (mg/cm2). Some controversy exists over the usefulness of SPF measurements, especially whether the 2 mg/cm2 application rate is an accurate reflection of people’s actual use.

Newer sunscreens have been developed with the ability to withstand contact with water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 and sweat
SWEAT
SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...

.

Sun protection factor (SPF)



The sun protection factor of a sunscreen is a laboratory measure of the effectiveness of sunscreen — the higher the SPF, the more protection a sunscreen offers against UV-B (the ultraviolet radiation that causes sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

).

The SPF is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, as a multiple of the amount required without the sunscreen. There is a popular oversimplification of how SPF determines how long one can stay in the sun. For example, many users believe that, if they normally get sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun fifteen hours (i.e. fifteen times longer) without getting sunburn. This would be true if the intensity of UV radiation were the same for the whole fifteen hours as in the one hour, but this is not normally the case. Intensity of solar radiation varies considerably with time of day. During early morning and late afternoon, the sun's radiation intensity is diminished since it must pass through more of the Earth's atmosphere while it is near the horizon.

In practice, the protection from a particular sunscreen depends, besides on SPF, on factors such as:
  • The skin type
    Human skin color
    Human skin color is primarily due to the presence of melanin in the skin. Skin color ranges from almost black to white with a pinkish tinge due to blood vessels underneath. Variation in natural skin color is mainly due to genetics, although the evolutionary causes are not completely certain...

     of the user.
  • The amount applied and frequency of re-application.
  • Activities in which one engages (for example, swimming leads to a loss of sunscreen from the skin).
  • Amount of sunscreen the skin has absorbed.


The SPF is an imperfect measure of skin damage because invisible damage and skin aging are also caused by ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 type A (UVA, wavelength 320 to 400 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...

), which does not cause reddening or pain. Conventional sunscreen blocks very little UVA radiation relative to the nominal SPF; broad spectrum sunscreens are designed to protect against both UVB and UVA. According to a 2004 study, UVA also causes DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 damage to cells deep within the skin, increasing the risk of malignant melanomas. Even some products labeled "broad-spectrum UVA/UVB protection" do not provide good protection against UVA rays. The best UVA protection is provided by products that contain zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

, avobenzone
Avobenzone
Avobenzone is an oil soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays....

, and ecamsule
Ecamsule
Ecamsule is an organic compound which is added to many sunscreens to filter out UVA rays...

. Titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

 probably gives good protection, but does not completely cover the entire UV-A spectrum, as recent research suggests that zinc oxide is superior to titanium dioxide at wavelengths between 340 and 380 nm.

Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions are in force in several countries. In the EU sunscreen labels can only go up to SPF 50+ (actually indicating a SPF of 60 or higher) while Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

's upper limit is 30+. The United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 does not have mandatory, comprehensive sunscreen standards, although a draft rule has been under development since 1978. In the 2007 draft rule, Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 (FDA) proposed to institute the labelling of SPF 50+ for sunscreens offering more protection. This and other measures were proposed to limit unrealistic claims about the level of protection offered (such as "all day protection").

The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source. In the US, such an in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

test is required by the FDA
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

. It can also be measured in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

with the help of a specially designed spectrometer
Spectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...

. In this case, the actual transmittance
Transmittance
In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. A related term is absorptance, or absorption factor, which is the fraction of radiation absorbed by a sample at a specified wavelength...

 of the sunscreen is measured, along with the degradation of the product due to being exposed to sunlight. In this case, the transmittance of the sunscreen must be measured over all wavelengths in the UV-B range (290–320 nm), along with a table of how effective various wavelengths are in causing sunburn (the erythemal action spectrum) and the actual intensity spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

 of sunlight (see the figure). Such in vitro measurements agree very well with in vivo measurements.
Numerous methods have been devised for evaluation of UVA and UVB protection. The most reliable spectrophotochemical methods eliminate the subjective nature of grading erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...

.

Mathematically, the SPF is calculated from measured data as
where is the solar irradiance spectrum, the erythemal action spectrum, and the monochromatic protection factor, all functions of the wavelength . The MPF is roughly the inverse of the transmittance at a given wavelength.

The above means that the SPF is not simply the inverse of the transmittance in the UV-B region. If that were true, then applying two layers of SPF 5 sunscreen would be equivalent to SPF 25 (5 times 5). The actual combined SPF is always lower than the square of the single-layer SPF.

Persistent pigment darkening (PPD)


The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring UVB light protection. Originally developed in Japan, it is the preferred method used by manufacturers such as L'Oréal
L'Oréal
The L'Oréal Group is the world's largest cosmetics and beauty company. With its registered office in Paris and head office in the Paris suburb of Clichy, Hauts-de-Seine, France, it has developed activities in the field of cosmetics...

.

Instead of measuring erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...

 or reddening of the skin, the PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. The PPD method is an in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

test like SPF. In addition, Colipa has introduced a method which, it is claimed, can measure this in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

and provide parity with the PPD method.
As part of revised guidelines for sunscreens in the EU, there is a requirement to provide the consumer with a minimum level of UVA protection in relation to the SPF. This should be a UVA PF of at least 1/3 of the SPF to carry the UVA seal. The implementation of this seal is in its phase-in period, so a sunscreen without it may already offer this protection.

Star rating system


In the UK and Ireland, the Boots star rating system is a proprietary in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

method used to describe the ratio of UVA to UVB protection offered by sunscreen creams and sprays. Based on original work by Prof. Brian Diffey at Newcastle University, the Boots Company in Nottingham, UK, developed a standard method which has been adopted by most companies marketing these products in the UK. The logo
Logo
A logo is a graphic mark or emblem commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition...

 and methodology of the test are licenced for a token fee to any manufacturer or brand of sunscreens that are sold in the Boots retail chain, provided the products to which the logo is applied perform to the standard claimed. Own Label products exclusively sold in other retailers are now excluded from the terms of the licence.
It should not be confused with SPF, which is measured with reference to burning and UVB. One-star products provide the least ratio of UVA protection; five-star products are best. The method has recently been revised in the light of the Colipa UVA PF test, and with the new EU recommendations regarding UVA PF. The method still uses a spectrophotometer to measure absorption of UVA vs UVB; the difference stems from a requirement to pre-irradiate samples (where this was not previously required) to give a better indication of UVA protection, and of photostability when the product is used. With the current methodology, the lowest rating is three stars, the highest being five stars.

In August 2007, the FDA put out for consultation the proposal that a version of this protocol be used to inform users of American product of the protection that it gives against UVA

Sunblock is a type of sunscreen


Sunblock typically refers to opaque sunscreen that is effective at blocking both UVA and UVB rays and uses a heavy carrier oil to resist being washed off. Titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

 and zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

 are two of the important ingredients in sunblock. Unlike the organic sun-blocking agents used in many sunscreens, these metal oxides do not degrade with exposure to sunlight.

The use of the word "sunblock" in the marketing of sunscreens is controversial. The FDA has considered banning such use because it can lead consumers to overestimate the effectiveness of products so labeled.

For total protection against damage from the sun, the skin needs to be protected from UVA, UVB and IRA (infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 light). Roughly 35% of solar energy is IRA.

Potential health risks


As a defense against UV radiation, the amount of the brown pigment melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

 in the skin increases when exposed to moderate (depending on skin type
Human skin color
Human skin color is primarily due to the presence of melanin in the skin. Skin color ranges from almost black to white with a pinkish tinge due to blood vessels underneath. Variation in natural skin color is mainly due to genetics, although the evolutionary causes are not completely certain...

) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB on the other hand yields a tan that takes roughly two days to develop because it stimulates the body to produce more melanin. The photochemical properties of melanin make it an excellent photoprotectant
Photoprotection
Photoprotection is a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation...

.

Sunscreen chemicals on the other hand cannot dissipate the energy of the excited state as efficiently as melanin and therefore the penetration of sunscreen ingredients into the lower layers of the skin increases the amount of free radicals and reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

 (ROS).

Some sunscreen lotions now include compounds such as titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

 which helps protect against UVB rays. Other UVA blocking compounds found in sunscreen include zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

 and avobenzone
Avobenzone
Avobenzone is an oil soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays....

. There are also naturally occurring compounds found in rainforest plants that have been known to protect the skin from UV radiation damage, such as the fern Phlebodium aureum
Phlebodium aureum
Phlebodium aureum is an epiphytic fern native to tropical and subtropical regions of the Americas...

.

Some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen which penetrates through the stratum corneum
Stratum corneum
The stratum corneum is the outermost layer of the epidermis, consisting of dead cells that lack nuclei and organelles. The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress...

 may or may not be large enough to cause damage. In one study of sunscreens, the authors write:

The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.


In an experiment by Hanson et al. that was published in 2006, the amount of harmful reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

 was measured in untreated and in sunscreen-treated skin. In the first 20 minutes the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin.

George Zachariadis and E Sahanidou of the Laboratory of Analytical Chemistry, at Aristotle University, in Thessaloniki, Greece, have now carried out an ICP-AES
ICP-AES
Inductively coupled plasma atomic emission spectroscopy , also referred to as inductively coupled plasma optical emission spectrometry , is an analytical technique used for the detection of trace metals...

 analysis of several commercially available sunscreen creams and lotions. "The objective was the simultaneous determination of titanium and several minor, trace or toxic elements (aluminum, zinc, magnesium, iron, manganese, copper, chromium, lead, and bismuth) in the final products," the researchers say. They concluded that "Most of the commercial preparations that were studied showed generally good agreement to the ingredients listed on the product label." However, they also point out that the quantitative composition of the products tested cannot be assessed because the product labels usually do not provide a detailed break down of all ingredients and their concentrations. They also point out that, worryingly, their tests consistently revealed the presence of elements not cited in the product formulation, which emphasized the need for a standardized and official testing method for multi-element quality control of these products.

Some epidemiological studies indicate an increased risk of malignant melanoma for the sunscreen user. Despite these studies, no medical association has published recommendations to not use sunblock. Different meta-analysis
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...

 publications have concluded that the evidence is not yet sufficient to claim a positive correlation between sunscreen use and malignant melanoma.

Adverse health effects may be associated with some synthetic compounds in sunscreens. In 2007 two studies by the CDC highlighted concerns about the sunscreen chemical oxybenzone (benzophenone-3). The first detected the chemicals in greater than 95% of 2000 Americans tested, while the second found that mothers with high levels of oxybenzone in their bodies were more likely to give birth to underweight baby girls.

Concerns have been raised regarding the use of nanoparticles in sunscreen. Theoretically, sunscreen nanoparticles could increase rates of certain cancers, or diseases similar to those caused by asbestos.
In 2006 the Therapeutic Goods Administration of Australia concluded a study and found:

"There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free radical formation in the presence of light and that this may damage these cells (photo-mutagenicity with zinc oxide). However, this would only be of concern in people using sunscreens if the zinc oxide and titanium dioxide penetrated into viable skin cells. The weight of current evidence is that they remain on the surface of the skin and in the outer dead layer (stratum corneum) of the skin."

Vitamin D


The use of sunscreen interferes with vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

 production, leading to deficiency in Australia after a government campaign to increase sunscreen use. Doctors recommend spending small amounts of time in the sun without sun protection to ensure adequate production of vitamin D. When the UV index
UV index
The ultraviolet index or UV Index is an international standard measurement of the strength of the ultraviolet radiation from the sun at a particular place on a particular day...

 is greater than 3 (which occurs daily within the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 and daily during the spring and summer seasons in temperate regions) adequate amounts of vitamin D3 can be made in the skin after only ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen. With longer exposure to UVB rays, an equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is generated.

Active ingredients


The principal ingredients in sunscreens are usually aromatic
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 molecules conjugated
Conjugated system
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...

 with carbonyl
Carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....

 groups. This general structure allows the molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays from reaching the skin. So, upon exposure to UV light, most of the ingredients (with the notable exception of avobenzone
Avobenzone
Avobenzone is an oil soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays....

) do not undergo significant chemical change, allowing these ingredients to retain the UV-absorbing potency without significant photodegradation
Photodegradation
Photodegradation is degradation of a photodegradable molecule caused by the absorption of photons, particularly those wavelengths found in sunlight, such as infrared radiation, visible light, and ultraviolet light. However, other forms of electromagnetic radiation can cause photodegradation...

. A chemical stabilizer is included in some sunscreens containing avobenzone to slow its breakdown - examples include formulations containing Helioplex
Helioplex
Helioplex is a formulation of broad-spectrum ultraviolet skin protection containing avobenzone and oxybenzone made by Neutrogena....

 and AvoTriplex. The stability of avobenzone can also be improved by bemotrizinol
Bemotrizinol
Bemotrizinol is an oil-soluble organic compound that is added to sunscreens to absorb UV rays. It is marketed as Tinosorb S by BASF and as Escalol S by International Specialty Products. A recent development is Tinosorb S Aqua, which is bemotrizinol in a PMMA matrix dispersed in water...

, octocrylene
Octocrylene
Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of a diphenylcyanoacrylate with 2-ethylhexanol...

 and various other photostabilisers.

FDA allowable ingredients


The following are the FDA allowable active ingredients in sunscreens:
UV-filter Other names Maximum concentration Permitted in these countries Results of safety testing
p-Aminobenzoic acid PABA 15% (5% EC-will be banned from sale to consumers from 8 October 2009) EC, USA, AUS Protects against skin tumors in mice. Shown to increase DNA defects, however, and is now less commonly used.
Padimate O OD-PABA, octyldimethyl-PABA, σ-PABA 8% (EC,USA,AUS) 10% (JP)
(Not currently supported in EU and may be delisted)
EC, USA, AUS, JP Not tested
Phenylbenzimidazole sulfonic acid
Phenylbenzimidazole sulfonic acid
Phenylbenzimidazole sulfonic acid is a common sunscreen agent. In 1999, the United States Food and Drug Administration regulated that the name ensulizole be used on sunscreen labels in the United States. Phenylbenzimidazole sulfonic acid is primarily a UVB protecting agent providing only minimal...

Ensulizole, Eusolex 232, PBSA, Parsol HS 4% (US,AUS) 8% (EC) 3% (JP) EC,USA, AUS, JP Genotoxic in bacteria
Cinoxate
Cinoxate
Cinoxate is an organic compound used as an ingredient in some types of sunscreens. It is an ester formed from methoxycinnamic acid and 2-ethoxyethanol. It is a slightly yellow viscous liquid that is insoluble in water, but miscible with alcohols, esters, and vegetable oils.It protects skin...

2-Ethoxyethyl p-methoxycinnamate 3% (US) 6% (AUS) USA, AUS Not tested
Dioxybenzone
Dioxybenzone
Dioxybenzone is an organic compound used in sunscreen to block UVB and short-wave UVA rays. It is a derivative of benzophenone. It is a yellow powder with a melting point of 68 °C. It is insoluble in water, but moderately soluble in ethanol and isopropanol....

Benzophenone-8 3% USA, AUS Not tested
Oxybenzone
Oxybenzone
Oxybenzone is an organic compound used in sunscreens. It forms colorless crystals that are readily soluble in most organic solvents. A 2008 study by the US Centers for Disease Control and Prevention found the compound to be present in 96.8% of human urine samples analyzed as part of the...

Benzophenone-3, Eusolex 4360, Escalol 567 6% (US) 10% (AUS,EU) 5% (JP) EC, USA, AUS, JP Not tested
Homosalate Homomethyl salicylate, HMS 10% (EC, JP) 15% (US,AUS) EC, USA, AUS, JP Not tested
Menthyl anthranilate Meradimate 5% USA, AUS Not tested
Octocrylene
Octocrylene
Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of a diphenylcyanoacrylate with 2-ethylhexanol...

Eusolex OCR, 2-cyano-3,3diphenyl acrylic acid, 2-ethylhexylester 10% EC,USA, AUS, JP Increases ROS
Octyl methoxycinnamate
Octyl methoxycinnamate
Octyl methoxycinnamate or octinoxate , trade names Eusolex 2292 and Uvinul MC80, is an organic compound that is an ingredient in some sunscreens and lip balms. It is an ester formed from methoxycinnamic acid and 2-ethylhexanol...

Octinoxate, EMC, OMC, Ethylmethoxycinnamate, Escalol 557, 2-ethylhexyl-paramethoxycinnamate, Parsol MCX 7.5% (US) 10% (EC,AUS)20% (JP) EC,USA, AUS, JP
Octyl salicylate Octisalate, 2-Ethylhexyl salicylate, Escalol 587, 5% (EC,USA,AUS) 10% (JP) EC,USA, AUS, JP Not tested
Sulisobenzone
Sulisobenzone
Sulisobenzone is an ingredient in some sunscreens which protects the skin from damage by UVB and short-wave UVA ultraviolet light.Its sodium salt, sulisobenzone sodium, is also referred to as benzophenone-5....

2-Hydroxy-4-Methoxybenzophenone-5-sulfonic acid,
3-benzoyl-4-hydroxy-6-methoxybenzenesulfonic acid, Benzophenone-4, Escalol 577
5% (EC) 10% (US, AUS, JP) EC,USA, AUS, JP
Trolamine salicylate
Trolamine salicylate
Trolamine salicylate is an organic compound which is the salt formed between triethanolamine and salicylic acid.It is used as an ingredient in sunscreens, analgesic creams, and cosmetics. The salicylic acid portion contributes to both the sun protection effect and to the analgesic effect. The...

Triethanolamine salicylate 12% USA, AUS Not tested
Avobenzone
Avobenzone
Avobenzone is an oil soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays....

1-(4-methoxyphenyl)-3-(4-tert-butyl
phenyl)propane-1,3-dione, Butyl methoxy dibenzoylmethane, BMDBM, Parsol 1789, Eusolex 9020
3% (US) 5% (EC,AUS)10% (JP) EC, USA, AUS, JP Not available
Ecamsule
Ecamsule
Ecamsule is an organic compound which is added to many sunscreens to filter out UVA rays...

Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid 10% EC,AUS (US:Approved in certain formulations up to 3% via New Drug Application (NDA) Route) Protects against skin tumors in mice
Titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

CI77891 25% (No limit Japan) EC,USA, AUS, JP Not tested
Zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

25% (US) 20% (AUS)
(EC-25% provided particle size >100 nm)
(Japan, No Limit)
EC,USA, AUS, JP Protects against skin tumors in mice


Other ingredients approved within the EU and other parts of the world, which have not been included in the current FDA Monograph:
UV-filter Other names Maximum concentration Permitted in
4-Methylbenzylidene camphor
4-Methylbenzylidene camphor
4-Methylbenzylidene camphor is an organic camphor derivative that is used in the cosmetic industry for its ability to protect the skin against UV, specifically UV B radiation. As such it is used in sunscreen lotions and other skincare products claiming a SPF value...

Enzacamene, Parsol 5000, Eusolex 6300, MBC 4%* EC, AUS
Tinosorb M
Bisoctrizole
Bisoctrizole is a benzotriazole-based organic compound that is added to sunscreens to absorb UV rays....

Bisoctrizole, Methylene Bis-Benzotriazolyl Tetramethylbutylphenol, MBBT 10%* EC, AUS, JP
Tinosorb S
Bemotrizinol
Bemotrizinol is an oil-soluble organic compound that is added to sunscreens to absorb UV rays. It is marketed as Tinosorb S by BASF and as Escalol S by International Specialty Products. A recent development is Tinosorb S Aqua, which is bemotrizinol in a PMMA matrix dispersed in water...

Bis-ethylhexyloxyphenol methoxyphenol triazine, Bemotrizinol, BEMT, anisotriazine 10% (EC, AUS) 3% (JP)* EC, AUS, JP
Neo Heliopan AP
Bisdisulizole disodium
Bisdisulizole disodium is a water soluble organic compound which is added to sunscreens to absorb UVA rays...

Bisdisulizole Disodium, Disodium phenyl dibenzimidazole tetrasulfonate, bisimidazylate, DPDT 10% EC, AUS
Mexoryl XL
Drometrizole trisiloxane
Drometrizole trisiloxane is a lipophilic benzotriazole derivative marketed as Mexoryl XL by L'Oréal and is used in sunscreens to absorb UV radiation. It is a broad-spectrum UV absorber with two absorption peaks, one at 303 nm and one at 344 nm . Just like Mexoryl SX , it is used exclusively in...

Drometrizole Trisiloxane 15% EC, AUS
Benzophenone-9 Uvinul DS 49, CAS 3121-60-6, Sodium Dihydroxy Dimethoxy Disulfobenzophenone 10% JP
Uvinul T 150
Ethylhexyl triazone
Ethylhexyl triazone is an organic compound used in sunscreens to absorb UVB radiation. It is marketed as Uvinul T 150 by BASF. Ethylhexyl triazone has an absorption maximum of 314 nm....

Octyl triazone, ethylhexyl triazone, EHT 5% (EC, AUS) 3% (JP)* EC, AUS
Uvinul A Plus
Diethylamino hydroxybenzoyl hexyl benzoate
Diethylamino hydroxybenzoyl hexyl benzoate is an organic compound used in sunscreens to absorb UVA radiation. It is marketed as Uvinul A Plus by BASF...

Diethylamino Hydroxybenzoyl Hexyl Benzoate 10% (EC,JP) EC , JP
Uvasorb HEB
Iscotrizinol
Iscotrizinol is an organic compound used in sunscreens to absorb UVA and UVB radiation. It is marketed as Uvasorb HEB by 3V Sigma....

Iscotrizinol, Diethylhexyl butamido triazone, DBT 10% (EC) 5% (JP) * EC, JP
Parsol SLX
Polysilicone-15
Polysilicone-15 is an organic compound used in hair products like shampoos, conditioners, hair sprays, pomades and color treatment products to absorb UVB radiation. In the EU, it is also approved for use in sunscreens and cosmetics. The absorption maximum is at about 310 nm. It is marketed as...

Dimethico-diethylbenzalmalonate, Polysilicone-15 10% EC, AUS, JP
Isopentenyl-4-methoxycinnamate Isoamyl p-Methoxycinnamate, IMC, Neo Heliopan E1000, Amiloxate 10% * EC, AUS


Many of the ingredients not approved by the FDA are relatively new and developed to absorb UVA.

* Time and Extent Application (TEA), Proposed Rule on FDA approval expected 2009

Application



Excessive exposure to direct sunlight is potentially harmful. Excessive exposure can result in sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

 if a person does not wear sun protective clothing
Sun protective clothing
Sun protective clothing is clothing specifically designed for sun protection and is produced from a fabric rated for its level of ultraviolet protection. A novel weave structure and denier may produce sun protective properties...

 or use suitable sunscreen. Products with a higher SPF (Sun Protection Factor) level provide greater protection against ultraviolet radiation. However in 1998, the Annual Meeting of the American Association for the Advancement of Science
American Association for the Advancement of Science
The American Association for the Advancement of Science is an international non-profit organization with the stated goals of promoting cooperation among scientists, defending scientific freedom, encouraging scientific responsibility, and supporting scientific education and science outreach for the...

 reported that some sunscreens advertising UVA and UVB protection do not provide adequate safety from UVA radiation and could give sun tanners a false sense of protection. A sunscreen should also be hypoallergenic and noncomedogenic so it doesn't cause a rash or clog the pores, which can cause acne.

For those who choose to tan, some dermatologists recommend the following preventative measures:
  • Sunscreens should block both UVA and UVB rays. These are called broad-spectrum sunscreens, which should also be hypoallergenic and noncomedogenic so it doesn't cause a rash or clog the pores, which can cause acne.
  • Sunscreens need to be applied thickly enough to get the full SPF protection.
  • Sunscreens should be applied 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after the sun exposure begins. Further reapplication is only necessary after activities such as swimming, sweating, and rubbing.
  • Sun rays are strongest between 10 am and 4 pm. Sun rays are stronger at higher elevation
    Elevation
    The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....

    s (mountains) and latitude
    Latitude
    In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

    s near the equator
    Equator
    An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

    .
  • Wearing a hat with a brim and anti-UV sunglasses can provide almost 100% protection against ultraviolet radiation entering the eyes.
  • Reflective surfaces like snow and water can greatly increase the amount of UV radiation to which the skin is exposed.


Recent evidence indicates that caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...

 and caffeine sodium benzoate increase UVB-induced apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

 both in topical and oral applications. In mice, UVB-induced hyperplasia
Hyperplasia
Hyperplasia means increase in number of cells/proliferation of cells. It may result in the gross enlargement of an organ and the term is sometimes mixed with benign neoplasia/ benign tumor....

 was greatly reduced with administration of these substances. Although studies in humans remain untested, caffeine and caffeine sodium benzoate may be novel inhibitors of skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...

.

External links