DEET (DEET), also known as dioxin, dioxin, DEET, is a light yellow liquid and oily substance. It is a common anti-mosquito liquid ingredient. Mosquito. DEET also prevents tick bites, some rickettsial diseases, tick-borne encephalitis and other tick-borne diseases such as Lyme disease. It can also prevent mosquito-mediated pathogens such as dengue fever, malaria, West Nile virus, and eastern equine encephalitis virus.