Technically speaking, its chemical name is N, N-diethyl-meta-toluamide.
But more practically speaking, it's the stuff that keeps insects away. And it does it extremely well. When looking at DEET repellents, you'll notice that they are available with varying percentage levels of DEET. A common misconception is that the higher the DEET percentage, the stronger the coverage. Not so. Whether you're using 25%, 100% or something in between, all DEET repellents will give you the same great coverage when applied. The difference is in the longevity. Each percentage of DEET corresponds to how long the protection will last. For example, a 25% DEET will provide six hours of protection while a 100% DEET will provide ten hours of protection.
Over the years, numerous studies have been conducted regarding the health-effects of contact with DEET for short-term, long-term and human exposure. The results show there are no unreasonable adverse effects to people or the environment with the normal use of DEET products