Mosquito repellents are important tools for prevention of insect-borne diseases as well as painful or uncomfortable insect bites. The 2 most effective and widely used products are N, N-diethyl-3-methylbenzamide (deet), which is applied to exposed skin, and permethrin, which is applied to clothes. Both are safe when used according to directions. Other repellents, including a variety of plant-derived products, have also been used but generally have a weaker or shorter-lived repellent effect.  Insect repellents are important public health tools for the prevention of vector-borne infectious diseases. Technically, an insect repellent is any chemical -- natural or synthetic -- that causes insects or other arthropods to make directed, oriented movements away from the source of repellent.   Many conventional mosquito repellents contain the active ingredients DEET or picaridin. But there are more natural mosquito repellents available that may also work well.  If you live in an area where mosquitoes are more a mild nuisance, plant-based mosquito repellents often work just fine. They may be a reasonable alternative to conventional mosquito repellents. But if you live in an area that is heavy with mosquitoes or you are prone to bites, you may not want to take any chances. Conventional mosquito repellents containing higher concentrations (23.8%) of DEET or picaridin offer the best protection.