insect repellent, substance applied to the skin in order to provide protection against biting insects, primarily mosquitoes, ticks, chiggers, fleas, and certain flies. The most effective such substance is DEET (N,N-diethyl-meta-toluamide), which blocks insect odor receptors for several compounds in human sweat. DEET is a common ingredient in many commercially available insect repellents; picaridin is also effective. Citronella oil, eucalyptus oil, soybean oil, and other substances also repel biting insects, although they are typically effective for a much shorter period of time than DEET is. Permethrin, a persistent contact insecticide that is poorly absorbed by humans, is used to treat clothing, bedding, and the like to protect against mosquitoes and ticks. The use of insect repellents is often recommended in certain locales because it reduces the likelihood of acquiring malaria, Lyme disease, and other infections spread by biting insects. Repellents do not protect against bees and other stinging insects.