Androgenic alopeciaAlopecia or hair loss is the medical description of the loss of hair from the head or body, sometimes to the extent of baldness. Unlike the common aesthetic depilation of body hair, alopecia tends to be involuntary and unwelcome, e.g., androgenic alopecia...
(also known as
androgenetic alopecia or
alopecia androgenetica) is a common form of
hair lossBaldness involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or "male pattern baldness" that occurs in adult male humans and other species...
in both female and male
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s,
chimpanzeeChimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
s, and
orangutanThe orangutans are two endangered species of great apes. Known for their intelligence, they live in trees and are the largest living arboreal animal. They have longer arms than other great apes, and their hair is typically reddish-brown, instead of the brown or black hair typical of other great apes...
s. In male humans in particular, this condition is also commonly known as
male pattern baldnessBaldness involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or "male pattern baldness" that occurs in adult male humans and other species...
. Hair is lost in a well-defined pattern, beginning above both temples. Hair also thins at the crown of the head. Often a rim of hair around the sides and rear of the head is left, or the condition may progress to complete baldness.
The pattern of hair loss in women differs from male pattern baldness.
Androgenic alopeciaAlopecia or hair loss is the medical description of the loss of hair from the head or body, sometimes to the extent of baldness. Unlike the common aesthetic depilation of body hair, alopecia tends to be involuntary and unwelcome, e.g., androgenic alopecia...
(also known as
androgenetic alopecia or
alopecia androgenetica) is a common form of
hair lossBaldness involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or "male pattern baldness" that occurs in adult male humans and other species...
in both female and male
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s,
chimpanzeeChimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
s, and
orangutanThe orangutans are two endangered species of great apes. Known for their intelligence, they live in trees and are the largest living arboreal animal. They have longer arms than other great apes, and their hair is typically reddish-brown, instead of the brown or black hair typical of other great apes...
s. In male humans in particular, this condition is also commonly known as
male pattern baldnessBaldness involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or "male pattern baldness" that occurs in adult male humans and other species...
. Hair is lost in a well-defined pattern, beginning above both temples. Hair also thins at the crown of the head. Often a rim of hair around the sides and rear of the head is left, or the condition may progress to complete baldness.
The pattern of hair loss in women differs from male pattern baldness. In women, the hair becomes thinner all over the head, and the hairline does not recede. Androgenic alopecia in women rarely leads to total baldness.
Cause
A variety of genetic and environmental factors likely play a role in causing androgenic alopecia. Although researchers are studying the factors that may contribute to this condition, most of these remain unknown. Researchers have determined that this form of hair loss is related to hormones called
androgenAndrogen is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics in vertebrates by binding to androgen receptors. This includes the activity of the accessory male sex organs and...
s, particularly an androgen called
dihydrotestosteroneDihydrotestosterone Full name: 5α-Dihydrotestosterone, abbreviating to 5α-DHT; INN: androstanolone is a biologically active metabolite of the hormone testosterone, formed primarily in the prostate gland, testes, hair follicles, and adrenal glands by the enzyme 5α-reductase by means of reducing the...
(DHT). Androgens are important for normal male sexual development before birth and during puberty. Androgens also have other important functions in both males and females, such as regulating hair growth and sex drive.
Male pattern baldness is caused by a genetic sensitivity of hair follicles to DHT, which causes them to shrink when exposed to it. This shortens their lifespan and prevents them from producing hair normally.
Hair loss and genetics
Much research has gone into the genetic component of male pattern baldness, or androgenic alopecia (AGA). Research indicates that susceptibility to premature male pattern baldness is largely X-linked. Other genes that aren’t sex linked are also involved.
Large studies in 2005 and 2007 stress the importance of the maternal line in the inheritance of male pattern baldness. German researchers name the androgen receptor gene as the cardinal prerequisite for balding. They conclude that a certain variant of the androgen receptor is needed for AGA to develop. In the same year the results of this study were confirmed by other researchers. This gene is recessive and a female would need two X chromosomes with the defect to show typical male pattern alopecia. Seeing that androgens and their interaction with the androgen receptor are the cause of AGA it seems logical that the androgen receptor gene plays an important part in its development.
Other research in 2007 suggests another gene on the X chromosome, that lies close to the androgen receptor gene, is an important gene in male pattern baldness. They found the region Xq11-q12 on the X-chromosome to be strongly associated with AGA in males. They point at the EDA2R gene as the gene that is mostly associated with AGA.
Other genes involved with hair loss have been found. One of them being a gene on chromosome 3. The gene is located at 3q26. This gene is recessive.
Another gene that might be involved in hair loss is the P2RY5. This gene is linked to hair structure. Certain variants can lead to baldness at birth, while another variant causes "
wooly hairWooly hair is the presence of Negroid hair on the scalp of persons of non-Negroid background, hair which, under the microscope, appears tightly coiled, and presents at birth or infancy usually as a solitary problem inherited in an autosomal dominant fashion.- See also :* Wooly hair nevus* Naxos...
."
In May 2009, researchers in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
identified a
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
,
Sox21Transcription factor SOX-21 is a protein that in humans is encoded by the SOX21 gene.-Further reading:...
, that appears to be responsible for hair loss in people.
Hormone levels correlated with androgenic alopecia
Men with androgenic alopecia typically have lower levels of total
testosteroneTestosterone is a steroid hormone from the androgen group. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands. It is the principal male sex hormone and an anabolic steroid.In men,...
, higher levels of unbound/free testosterone, and higher levels of total free androgens including DHT.
5-alpha-reductase is responsible for converting free testosterone into DHT. The genes for 5-alpha-reductase are known. The enzymes are present predominantly in the scalp and prostate. Levels of 5alpha-reductase are one factor in determining levels of DHT in the scalp and drugs which interfere with 5alpha-reductase (such as
finasterideFinasteride is a synthetic antiandrogen that acts by inhibiting type II 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone...
, which inhibits the predominant type 2 isoform) have been approved by the FDA as treatments for hair loss.
Sex hormone binding globulin (SHBG), which is responsible for binding testosterone and preventing its bioavailability and conversion to DHT, is typically lower in individuals with high DHT. SHBG is downregulated by insulin.
Increased levels of Insulin Growth Factor-1 (IGF-1) have been correlated to vertex balding.
High insulin levels seem the likely link between
metabolic syndromeMetabolic syndrome is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. It affects one in five people, and prevalence increases with age...
and baldness. Low levels of SHBG in men and non-pregnant women are also correlated with glucose intolerance and diabetes risk, though this correlation disappears during pregnancy.
Hair loss and lifestyle
While genetic factors seem to play the principal role in the development and progression of androgenic alopecia, lifestyle also plays a minor role as demonstrated by the vast increase in male and female pattern baldness in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
after
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
. Pattern baldness (androgenic alopecia) was either rare or non-existent among
hunter-gathererA hunter-gatherer society is one whose primary subsistence method involves the direct procurement of edible plants and animals from the wild, foraging and hunting without significant recourse to the domestication of either...
and other, less westernized societies eating in their traditional manner.
One study did show that free testosterone is lower 24 hours after intense aerobic exercise in men who already have high endurance but it was not investigated whether that level remains lowered beyond that point, or whether that lowering affects male pattern baldness in any way. It has been suggested that weight training may have a detrimental effect on hair by increasing testosterone levels; however, there is at least one study that indicates a decline in free testosterone as result of weight training.
Evolutionary theories of Male Pattern Baldness
One theory, advanced by Muscarella and Cunningham[4], suggests baldness evolved in males through sexual selection as an enhanced signal of aging and social maturity, whereby aggression and risk-taking decrease and nurturing behaviours increase. This may have conveyed a male with enhanced social status but reduced physical threat, which could enhance ability to secure reproductive partners and raise offspring to adulthood.
In a study by Muscarella and Cunnhingham [4], males and females viewed 6 male models with different levels of facial hair (beard and mustache or none) and cranial hair (full head of hair, receding and bald). Participants rated each combination on 32 adjectives related to social perceptions. Males with facial hair and those with bald or receding hair were rated as being older than those who were clean-shaven or had a full head of hair. Beards and a full head of hair were seen as being more aggressive and less socially mature, and baldness was associated with more social maturity. A review of social perceptions of male pattern baldness has been provided by Henss (2001) [5] .
The assertion that male pattern baldness is intended to convey a social message is supported by the fact that pattern baldness is also common in other primates, and is often used to convey increased status and maturity.
Gorillas evolved anatomically enlarged foreheads for this reason. This suggests that baldness could have evolved to enhance the apparent size of the forehead, and increase the area of the face to be displayed. It should also be noted that most ancestry primates had a shorter life-span, and as baldness usually occurs at a later stage in life, baldness could have been a sign of survival and longevity. Premature baldness could also have evolved in younger males to convey this message, which correlates with studies suggesting men with bald or receding hairlines were rated as older than those with a full head of hair.
Other evolutionary hypotheses include genetic linkage to beneficial traits unrelated to hair loss and
genetic driftGenetic drift or allelic drift is the change in the relative frequency with which a gene variant occurs in a population due to random sampling and chance: the alleles in offspring are a random sample of those in the parents, and chance has a role in determining whether a given individual survives...
.
Diagnosis
Differential diagnosis involves eliminating other causes of hair loss (such as poisoning) and comparing the pattern of hair loss to a typical male pattern baldness progression.
Treatments
While many people with male pattern baldness choose to accept the condition as they accepted their hair color or shape, there are
baldness treatmentsMore than half of men are affected by male pattern baldness by age 50, and baldness treatments are estimated to be a US $1 billion per year industry. Since the 1980s, drug therapy has increasingly become a realistic management option for baldness for men and women...
which can reduce or halt hair loss, and in early stages or in rare cases, reverse it entirely. Treatments include:
- Minoxidil
Minoxidil is a vasodilator medication known for its ability to slow or stop hair loss and promote hair regrowth...
, the recommended second-line treatment
- Topical Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that is a psychoactive stimulant drug. Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819. He coined the term kaffein, a chemical compound in coffee, which in English became caffeine...
- Dutasteride
Dutasteride is a 5-alpha-reductase inhibitor, a drug which inhibits the conversion of testosterone into dihydrotestosterone . It is used to treat conditions caused by DHT, such as benign prostatic hyperplasia...
and KetoconazoleKetoconazole is a synthetic antifungal drug used to prevent and treat skin and fungal infections, especially in immunocompromised patients such as those with AIDS...
are also 5-alpha reductase5-Alpha reductase is an enzyme involved in steroid metabolism.-Function:It converts testosterone, the male sex hormone, into the more potent dihydrotestosterone:Note the major difference — the Δ4,5 double-bond on the A ring...
inhibitors, but as of 2009 have not been FDA-approved as hair loss treatments.
- LLLT, or Low Level Laser Therapy
See also
- Hamilton-Norwood scale
The progression of male pattern baldness is generally classified on the Hamilton-Norwood scale, which ranges from stages I to VII.This measurement scale was first introduced by Dr. James Hamilton in the 1950s and later revised and updated by Dr. O'Tar Norwood in the 1970s.-See also:*Ludwig scale of...
: The scale that rates the severity of androgenic alopecia in males.
- Ludwig scale
The progression of female pattern baldness is generally classified on the Ludwig scale, which ranges from stages I to III.- External links :*...
: The scale that rates the severity of androgenic alopecia in females.
- Noncicatricial alopecia
-Causes:Causes of noncicatricial alopecia include:*Alopecia areata*Anagen effluvium*Androgenetic alopecia*Dermatopathia pigmentosa reticularis*Telogen effluvium*Trichotillomania...
External links