A gas made of nitrogen and hydrogen. It has a strong odor and can irritate the skin, eyes, nose, throat, and lungs. Ammonia is made by bacteria and decaying plants and animals and is found in water, soil, and air. Ammonia is also made by the body when proteins break down. In the laboratory, ammonia can be changed to a liquid and used in medicines, fertilizers, household cleaning liquids, and other products. It is also added to cigarettes to increase the effect of nicotine on the body.