N,N-diethylmetatoluamide, commonly called DEET, repels a variety of mosquitoes, chiggers, ticks, fleas, and biting flies; no topical repellent is effective against stinging insects such as bees and wasps. In the U.S., DEET is available in formulations of 5% through 40% and 100%. DEET products containing less than 20% can provide complete protection for 1-3 hours. Higher concentrations provide longer-lasting protection (up to 12 hours), but the duration of effect reaches a maximum at concentrations of 50%.

A long-acting DEET formulation, originally developed for the US Armed Forces is available in the US as Ultrathon® by 3M; it contains 25% or 33% DEET in a long-acting polymer formulation, which helps prevents loss from the skin surface. This product provides more than 95% protection against mosquito bites for 6 to 12 hours.

None of the presently marketed alternatives to DEET offer a similar duration of protection. Citronella-based repellents provide short-term protection against mosquitoes, but are probably ineffective against ticks. Studies are underway to test some of the newer non-DEET repellents.

An insecticide (not a repellent) known as permethrin, marketed as Repel Permanone® (and others), has been developed for application to clothing, mosquito nets, tents and sleeping bags to protect against both mosquitoes and ticks. Permethrin is more effective than DEET against ticks. Wearing permethrin-treated clothing and applying a DEET-containing repellent to the skin may be the most effective way to prevent insect bites. Treatment of clothing with permethrin can persist through 20 or more washing.