Biting insects have antennae that detect lactic acid, carbon dioxide, and other volatile compounds that humans and animals give off in their breath and from their skin. Mosquitoes are so sensitive to these chemicals that they can detect a potential blood meal from as far away as 100 feet! Insect repellents are believed to work by blocking the stimulation of these receptors, preventing insects from homing in on their source.
Why do almost all insect repellents contain the chemical DEET?
DEET has been used since 1957. Despite 40 years of testing more than 20,000 other compounds since then, DEET remains the most-effective and broad-spectrum repellent currently available.
I've heard recently about "time-release" DEET repellents. Do these products have any advantages over the other DEET repellents?
Nearly all DEET-based repellents on the market contain the DEET chemical simply mixed in a base of lotion, or alcohol. Extended or time-released products, in contrast, package the DEET in a special base that allows it to be released more slowly on to the skin surface. There are several advantages to this technology: These products will give longer-lasting protection, without requiring the use of high concentrations of DEET. They also reduce the number of times that re-application of the product may be necessary. Ultrathon™, which is a time-release product, contains 34.34% DEET in a polymer base; it is identical to the repellent used by the U.S. military.
How much repellent should I apply?
Insect repellent should be applied as a thin layer, covering all the exposed skin surface evenly. There is no need to saturate the skin in order for the repellent to be effective. Do not apply insect repellent over cuts, wounds, or inflamed or eczematous skin.
Is it O.K. to spray DEET on my clothes?
DEET can be applied to either exposed skin or clothing. It should not be applied to skin that is covered by clothes. DEET should also not be applied to synthetic fabrics such as rayon or to plastics, because it can damage these products.
I bought DEET-based wristbands, which claimed they would repel mosquitoes, but they don't seem to work. Why?
DEET only really protects the areas to which it is applied. Its repellent effect cannot travel far. The application of DEET to a few points of the body, therefore, will not "cloak" the user in protection. All exposed skin must be treated with DEET in order for it to be protected. Hungry insects will readily find any areas of unprotected skin.
I'm going to Africa. Which repellent should I bring with me?
When travelling to areas of the world where insect-transmitted diseases such as malaria, yellow fever and viral encephalitis are common, proper application of insect repellent is crucial to prevent the possibility of being infected. A DEET-based repellent will offer the best insurance against being bitten. Controlled-release DEET products may well be the ideal choice for the traveller looking for long-lasting protection without having to resort to using repellents with DEET concentrations over 35%. In general, citronella-based repellents would not provide adequate protection when travelling to these areas.
I've heard that DEET can cause seizures and neurological damage. Is that true?
Although it is true that there have been rare reports of seizures and neurological side effects associated with DEET use, it is important to realise how rare these reports are. The Environmental Protection Agency in the USA estimates that 200 million people use DEET repellent every year. After more than eight billion applications of DEET worldwide, there have been only 21 cases reported in the medical literature in which the use of DEET seemed to have been associated with the development of neurological toxicity. Six of these cases were a direct result of deliberate ingestion. Twelve of these 21 cases resolved completely, without any residual effects. When the EPA reviewed all available DEET human and animal neurotoxicity data in 1998, they concluded there was no evidence that DEET was a selective neurotoxin. Even if all the reported cases of neurological toxicity ascribed to DEET use were confirmed, the real-life risk of neurological side effects from DEET would be less than 1 in 100 million users.
I don't want to get a sunburn, and I want to protect myself from insect bites, too. Can I apply both sun screen and insect repellent to my skin?
Sunscreens and insect repellents may be used together on exposed skin. However, there is some evidence that DEET can reduce the efficacy of sunscreen when applied to the same area. One study showed as much as a 33% decrease in sun protection (SPF) when a 33% DEET lotion was simultaneously applied. Therefore, when applying both DEET repellent and a sunscreen, you will need to reapply the sunscreen more frequently to prevent sunburning. For the initial application onto dry skin, it is recommended to apply sun lotion first and allow to dry before applying insect repellent.