Liquid insect repellent is a chemical compound used to repel insects, such as mosquitoes. DEET is one of the most common active ingredients in insect repellents and is an acronym for N, N-diethyl-m-toluamide. It was developed by the U.S. Army in 1946 and has been used widely since then. DEET is effective against a wide range of insects, including ticks, fleas, and mosquitoes. It works by blocking the insect's sense of smell, making it difficult for them to locate their prey.