Deet inhibits cholinesterase. August 5, 2009. Deet, an insect repellent used by 200 million people a year, not only modifies insect behavior but also inhibits cholinesterase in insects and mammals, and interacts with the carbamate insecticides to increase their toxicity.
Title: Evidence for inhibition of cholinesterases in insect and mammalian nervous systems by the insect repellent deet. Vincent Corbel , Maria Stankiewicz , Cedric Pennetier , Didier Fournier , Jure Stojan , Emmanuelle Girard , Mitko Dimitrov , Jordi Molgo , Jean Marc Hougard  and Bruno Lapied.BMC Biology 2009, 7:47.Abstract. Full PDF.

Related: Popular Insect Repellent Deet Is Neurotoxic. ScienceDaily (Aug. 6, 2009) — The active ingredient in many insect repellents, deet, has been found to be toxic to the central nervous system. Researchers say that more investigations are urgently needed to confirm or dismiss any potential neurotoxicity to humans, especially when deet-based repellents are used in combination with other neurotoxic insecticides. [ See ]