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Mosquito on a bottle of herbal mosquito repellent.

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 Universitymarker states that, "Everglades National Parkmarker 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.

Within countries of the European Union, Implementation of Regulation 98/8/EC, commonly referred to as the Biocidal Products Directive, has severely limited the number and type of insect repellents available to European Consumers. Only a small number of active ingredients have been supported by manufacturers in submitting dossiers to the EU Authorities. In general, only formulations containing Deet, Picaridin (also known as Saltidin or Bayrepel) and Citridiol are available. Most "natural" insect repellents such as Citronella, Neem Oil, Herbal Extracts are no longer permitted for sale as insect repellents in the EU (Although this does not preclude them from being sold for "other" purposes, as long as the label does not indicate they are a biocide (insect repellent)

Insect repellents from natural sources

There are many preparations from naturally occurring sources that are repellent to certain insects. Some of these act as insecticides while others are only repellent.

Inactive substances

Essential oils such as geranium oil have no effect.

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 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?, and according to a review of scientific studies

See also



  1. Mishra AK, Singh N, Sharma VP, 1995 "Use of neem oil as a mosquito repellent in tribal villages of mandla district, madhya pradesh", Indian J Malariol, Sep;32(3):99-103 Pubmed
  2. "Test: Mosquito Repellents, The Verdict" Choice, The Australian Consumers Association
  3. Carroll SP, Loye J, 2006, Journal of the American Mosquito Control Association 22(3):507-514, 510
  4. Jeong-Kyu KIM, Chang-Soo KANG, Jong-Kwon LEE, Young-Ran KIM, Hye-Yun HAN, Hwa Kyung YUN, Evaluation of Repellency Effect of Two Natural Aroma Mosquito Repellent Compounds, Citronella and Citronellal, Entomological Research 35 (2), 117–120, 2005
  5. Ibrahim Jantan, and Zaridah Mohd. Zaki, Development of environment-friendly insect repellents from the leaf oils of selected Malaysian plants, ASEAN Review of Biodiversity and Environmental Conservation (ARBEC), May 1998.
  6. Trongtokit Y, Rongsriyan Y, Komalamisra N, Apiwathnasom L, Comparative repellency of 38 essential oils against mosquito bites, Phytother Res. 2005 Apr;19(4):303-9 [1]
  7. "Health Advisory: Tick and Insect Repellents", Information factsheet, Department of Health, New York State
  8. "Reregistration Eligibility Decision: DEET." U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances. September 1998. pp39-40
  9. Deet
  10. "So Then: Who’s Afraid of Citronella Oil? Update!" Cropwatch Newsletter Vol 2,Issue 1, No. 1
  12. Barnard, D.R. and R. Xue. 2004. Laboratory evaluation of mosquito repellents against Aedes albopictus, Culex nigripalpus, and Ochlerotatus triseriatus (Diptera: Culicidae). J. Med. Entomol. 41(4):726-730.
  13. BMJ Clinical Evidence
  14. [2]
  15. Insect bites and stings. DermNet NZ
  17. Lentek International-08/28/02
  18. Enayati AA, Hemingway J, Garner P., “Electronic mosquito repellents for preventing mosquito bites and malaria infection”, Cochrane Database Syst Rev., 2007 18; CD005434

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