Deet-free One major difference is DEETs corrosive properties, which can dissolve durable materials such as plastic, nylon and even paint. Imagine what it can do to your skin with prolonged use. Many synthetic insect repellents contain a harmful chemical called DEET. DEET chemical name, N,N-diethyl-meta-toluamide is the active ingredient in many repellent products, widely used to repel bugs such as mosquitoes and ticks. Rather than killing biting bugs, DEET works by masking our natural scent, making it hard for them to smell us. The Environmental Protection Agency EPA has tagged DEET as "slightly toxic", basing on its possible harm to your brain and organs when absorbed in certain amounts.