Ammonia (NH3) is an inorganic compound of nitrogen and hydrogen with a chemical formula of NH3. It is a colorless gas with a pungent odor that dissolves easily in water to form ammonium hydroxide solution. Ammonia is one of the most commonly produced industrial chemicals in the United States and is used in industry and commerce. It is also found naturally in humans, animals, and the environment.

Ammonia is essential for many biological processes and serves as a precursor for amino acid and nucleotide synthesis. In the environment, ammonia is part of the nitrogen cycle and is produced in soil from bacterial processes. About 80% of the ammonia produced by industry is used in agriculture as fertilizer. Ammonia is also used as a refrigerant gas, for purification of water supplies, and in the manufacture of plastics, explosives, textiles, pesticides, dyes, and other chemicals. It is found in many household and industrial-strength cleaning solutions.

Ammonia is highly soluble in water, and its exact solubility depends on temperature. Aqueous ammonia is also called ammonium hydroxide, but that molecule cannot be isolated. Ammonia is easily made in the laboratory by heating an ammonium salt, such as ammonium chloride, with a strong alkali, such as sodium hydroxide or calcium hydroxide.

Ammonia is a toxic gas that can cause irritation and burns. It interacts immediately upon contact with available moisture in the skin, eyes, oral cavity, respiratory tract, and particularly mucous surfaces to form the very caustic ammonium hydroxide. Ammonium hydroxide causes the necrosis of tissues through disruption of cell membrane lipids leading to cellular destruction. As cell proteins break down, water is extracted, resulting in an inflammatory response that causes further damage.