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Insect repellent
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An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects (and arthropods in general) from landing or climbing on that surface. There are also insect repellent products available based on sound production, particularly ultrasound (inaudibly high frequency sounds). These electronic devices have been shown to have no effect as a mosquito repellent by studies done by the EPA and many universities.
Insect repellents help prevent and control the outbreak of insect-borne diseases such as malaria, Lyme disease, Dengue fever, bubonic plague, and West Nile fever.
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An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects (and arthropods in general) from landing or climbing on that surface. There are also insect repellent products available based on sound production, particularly ultrasound (inaudibly high frequency sounds). These electronic devices have been shown to have no effect as a mosquito repellent by studies done by the EPA and many universities.
Insect repellents help prevent and control the outbreak of insect-borne diseases such as malaria, Lyme disease, Dengue fever, bubonic plague, and West Nile fever. Pest animals commonly serving as vectors for disease include the insects flea, fly, and mosquito; and the arachnid tick.
Common insect repellents include:
Usually insect repellents work by masking human scent, or by using a scent which insects naturally avoid. Permethrin is different in that it is actually a contact insecticide.
Repellent effectiveness
Synthetic repellents tend to be more effective and/or longer lasting than 'natural' repellents. However, some plant-based repellents are comparable to, or somewhat better than synthetics - depending on the formula. Essential oil repellents can be short-lived in their effectiveness, since essential oils can evaporate completely.
A test of various insect repellents by an independent consumer organization found that repellents containing DEET or picaridin are more effective than repellents with 'natural' active ingredients. All the synthetics gave almost 100% repellency for the first 2 hours, where the natural repellent products were most effective for the first 30-60 minutes, and required reapplication to be effective over several hours. However, some products in the market like essential oil candle and natural herb mosquito coil can give protection to an entire room up to 8 hours.
For protection against mosquitos, the U.S. Centers for Disease Control issued a statement in May 2008 recommending equally DEET, picaridin, oil of lemon eucalyptus and IR3535 for skin. Permethrin is recommended for clothing, gear, or bed nets. In an earlier report, the CDC found oil of lemon eucalyptus to be more effective than other plant-based treatments, with a similar effectiveness to low concentrations of DEET. However, a 2006 published study found in both cage and field studies that a product containing 40% oil of lemon eucalyptus was just as effective as products containing high concentrations of DEET. Research has also found that neem oil is mosquito repellent for up to 12 hours. Citronella oil's mosquito repellency has also been verified by research, including effectiveness in repelling Aedes aegypti, but requires reapplication after 30-60 minutes.
Repellent safety
Regarding safety with insect repellent use on children and pregnant women:
- Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater.
- Keep repellents out of the reach of children.
- Do not allow children to apply repellents to themselves.
- Use only small amounts of repellent on children.
- Do not apply repellents to the hands of young children because this may result in accidental eye contact or ingestion.
- Try to reduce the use of repellents by dressing children in long sleeves and long pants tucked into boots or socks whenever possible. Use netting over strollers, playpens, etc.
- As with chemical exposures in general, pregnant women should take care to avoid exposures to repellents when practical, as the fetus may be vulnerable.
Regardless of which repellent product used, it is recommended that the label is read before use and directions carefully followed. Usage instructions for repellents vary from country to country. Some insect repellents are not recommended for use on younger children.
In the DEET Reregistration Eligibility Decision (RED) the United States Environmental Protection Agency? (EPA) reported 14 to 46 cases of potential DEET associated seizures, including 4 deaths. The EPA states: "... it does appear that some cases are likely related to DEET toxicity," but observed that with 30% of the US population using DEET, the likely seizure rate is only about one per 100 million users.
The Pesticide Information Project of Cooperative Extension Offices of Cornell University states that, "Everglades National Park employees having extensive DEET exposure were more likely to have insomnia, mood disturbances and impaired cognitive function than were lesser exposed co-workers".
The EPA states that citronella oil shows little or no toxicity and has been used as a topical insect repellent for 60 years. However, the EPA also states that citronella may irritate skin and cause dermatitis in certain individuals. Canadian regulatory authorities concern with citronella based repellents is primarily based on data-gaps in toxicology, not on incidents.
Insect repellents from natural sources
There are many naturally occurring pesticides which can be used as an insect repellent, and some of these are:
- Achillea alpina (mosquitos)
- alpha-terpinene (mosquitos)
- Basil
- Callicarpa americana (Beautyberry)
- Camphor (moths)
- Carvacrol (mosquitos)
- Castor oil (mosquitos)
- Catnip oil (nepetalactone against mosquitos)
- Cedar oil (mosquitos)
- Celery extract (mosquitos)
- Cinnamon (leaf oil kills mosquito larvae)
- Citronella oil (repels mosquitos)
- Clove oil (mosquitos)
- Eucalyptus oil (70%+ eucalyptol), (cineol is a synonym), mosquitos, flies, dust mites)
- Fennel oil (mosquitos)
- Garlic (rice weevil, wheat flour beetle)
- Lemongrass
- Geranium oil (mosquitos)
- Lavender
- Lemon eucalyptus (Corymbia citriodora) essential oil and its active ingredient p-menthane-3,8-diol (PMD)
- Lemongrass oil (mosquitos)
- Marigolds
- Marjoram (Spider mites Tetranychus urticae and Eutetranychus orientalis)
- Neem oil (Repels or kills mosquitos, their larvae and a plethora of other insects including those in agriculture)
- Peppermint (mosquitos)
- Pennyroyal (Mentha pulegium) (mosquitos, fleas), but very toxic to pets.
- Rosemary (mosquitos)
- Spanish Flag Lantana camara (against Tea Mosquito Bug, Helopeltis theivora)
- Solanum villosum berry juice (against Stegomyia aegypti mosquitos)
- Tea tree
- Thyme (mosquitos)
Inactive substances
While soybean oil has no direct insect repellant activity, it is used as a fixative to extend the short duration of action of essential oils such as geranium oil in several commercial products.
Other commercial products offered for household mosquito "control" include small electrical mats, mosquito repellent vapor, DEET-impregnated wrist bands, and mosquito coils containing a form of the chemical allethrin. Mosquito-repellent candles containing citronella oil are sold widely in the U.S. All of these have been used with mixed reports of success and failure.
Less effective methods
Some old studies suggested that the ingestion of large doses of thiamin could be effective as a oral insect repellent against mosquito bites. However, there is now conclusive evidence that thiamin has no efficacy against mosquito bites.
Some claim that plants like wormwood or sagewort, lemon balm, lemon grass, lemon thyme and the mosquito plant (Pelargonium) will act against mosquitoes. However, scientists have determined that these plants are “effective” for a limited time only when the leaves are crushed and applied directly to the skin.
There are several, widespread, unproven theories about mosquito control such as the assertion that vitamin B, in particular B1 (thiamine), garlic, ultrasonic devices, incense, can be used to repel or control mosquitoes. Moreover, some manufacturers of "mosquito repelling" ultrasonic devices have been found to be fraudulent, and their devices were deemed "useless" in tests by the UK Consumer magazine Which? Application of other organic materials directly to the skin -- aloe vera, lime juice, and peppermint oil, for example -- is touted as somewhat effective, though the results have not been scientifically evaluated. One explanation is that such materials, with their strong odors, help mask the natural skin and sweat odors that initially attract mosquitos.
See also
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