Molecule of the Month

N,N-Diethyl-meta-toluamide

The search to find an effective insect repellent had its first success in the 1950s with the identification of synthetic agents. Much of the early testing was done by the U.S. Department of Agriculture using American soldiers in tropical and sub-tropical regions. Of the nearly 9,000 substances tested in 1954, N,N-diethyl-meta-toluamide (DEET) gave the best results. Since then more than 20,000 chemicals have been tested, but none have been as effective as DEET.

How does a mosquito locate its victim? Visual stimuli seem to be import at long ranges, but olfactory stimuli become more important as an insect nears its host. Mosquitoes have chemoreceptors on their antennae that are stimulated by carbon dioxide and lactic acid, which are end-products of our metabolism. A mosquito can detect carbon dioxide released from the skin at distances up to 36 meters.

DEET inhibits a mosquito's chemoreceptors. The proposed mechanism is that the repellent produces a layer of vapor a few millimeters thick just above the skin. An insect's sense of detection cannot penetrate this barrier. As a result, the insect cannot detect the wearer, and disorientation causes it to keep away.

DEET is an effective repellent, but it is toxic. In some individuals, it causes itching and swelling of the skin. If you experience these symptoms, you should stop using the product. A more serious problem is DEET's effect on the central nervous system. DEET is absorbed through the skin and can cause symptoms ranging from tremor, slurred speech and confusion to delusion, paranoia, convulsions and seizures. It is best to use a product with a lower concentration of DEET, and to shower after returning home.