In the great outdoors, it would hardly be practical (or desirable) to kill all the bugs around us. Instead, we just want them to leave us alone. Bug repellent sprays work by making us invisible or unattractive to insects such as mosquitoes, ticks, biting flies and chiggers, encasing us in our own temporary protective barrier.
The Centers for Disease Control and Prevention (CDC) recommends using insect repellents that have been registered with the EPA. Only products that the EPA has evaluated for safety and effectiveness can be EPA-registered, and as of July 2014, only the following active ingredients are used in EPA-registered skin-applied repellents [source: EPA]:
- catnip oil
- oil of citronella
- DEET (N,N-diethyl-meta-toluamide)
- IR3535 (3-[N-Butyl-N-acetyl]-aminopropionic acid)
- oil of lemon eucalyptus (p-Menthane-3,8-diol)
- 2-undecanone (also known as methyl nonyl ketone)
Of these, the CDC recommends products containing DEET, picaridin, IR3535 and oil of lemon eucalyptus for the longest-lasting protection against mosquitoes and other bugs. DEET is the most commonly used by far, with more than 500 EPA-registered bug repellents listing DEET as their active ingredient [source: EPA]. Found in brands like Off, Cutter and many others, DEET is sprayed directly onto skin or clothing. It works by interfering with insects' odor receptors, making it difficult for them to smell us [source: EPA, Howard Hughes Medical Institute].
Picaridin, found in 40 products including Sawyer and Natrapel brands, prevents mosquitoes and other insects from finding or recognizing their prey [sources: EPA, NPI C]. Like DEET and the others on the EPA-registered list, picaridin doesn't kill mosquitoes or other insects; it just keeps them away.
IR3535, found in Avon Skin-So-Soft products, is a proprietary formulation of the amino acid alanine [source: EPA]. Like catnip oil, oil of citronella and oil of lemon eucalyptus, IR3535 is classified as a biopesticide (as opposed to a conventional repellent), since it is derived from natural materials [source: University of Nebraska-Lincoln].
In addition to EPA-registered products, you may also encounter bug repellent sprays that are EPA-approved. These products contain ingredients such as cedar oil, geranium oil, peppermint oil or citronella oil (which is also found in some registered products), all classified as minimum risk pesticides [source: EPA]. But while the EPA has evaluated these products for safety, they have not been tested for effectiveness.