Although they might not have the best reputation, products that contain the chemicals DEET (N,N-diethyl-m-toluamide) or picaridin (KBR 3023) are the most effective insect repellents. While DEET is not a carcinogen, DEET products get a bad rap because long-term exposure may cause moodiness, insomnia and impaired cognitive function [source: Peterson]. Studies have shown that after high concentrations of continued exposure, DEET can cause hypertrophy of the liver and kidneys as well as stimulation of the central nervous system which can cause tremors and seizures [source: Extonet]. DEET products also have the potential to damage the water supply. DEET can not only harm aquatic life-forms, but it can also enter the drinking supply as runoff if farmers mishandle the product. The Environmental Protection Agency (EPA)monitors DEET products and only approves those that are effective and won't cause you or the environment damage.
Citing numerous scientific studies, the Centers for Disease Control and Prevention asserts that DEET products provide the longest-lasting protection against insects [source: CDC]. Depending on the amount of DEET in a product, it can repel insects for an average of three to eight hours [source: EPA].
Here's a guide for the length of time for the effectiveness of various DEET concentrations:
- 23.8 percent = 5 hours protection
- 20 percent = 4 hours protection
- 6.65 percent = 2 hours protection
- 4.75 percent = 1 hour of protection