DEET (N,N-Diethyl-meta-toluamide) is diethyltoluamide, an active ingredient of most insecticides. Developed in 1944 by Samuel Gertler, it was designed to combat insect stings and bites during jungle warfare of World War II in the Pacific.

It was used in the military as standard issue in tropical zones in 1946 and later released for commercial use in 1957.

Nicknamed "bug juice", the chemical was originally thought to deter the smelling ability of insects and reduce attacks. However, recent studies indicate that insects "dislike" the smell instead of the proposed retardant understanding.

DEET is a solvent that is corrosive to glass, plastics and other materials.

DEET is recommended in 30% concentration only in most countries as the health effects are still under investigation.

More Info: en.wikipedia.org