Ammonia is a colorless gas with an extremely sharp, choking smell that can burn your nose and throat. If you've ever opened a bottle of strong cleaning solution and had to turn your head away from the intense fumes, you've probably smelled ammonia.

Chemically, ammonia is made of nitrogen and hydrogen atoms bonded together. It dissolves easily in water, which is why household cleaners often contain ammonia dissolved in liquid form. These cleaners work well at cutting through grease and grime on windows, floors, and countertops, though the powerful smell means you need to open windows when using them.

Ammonia occurs naturally when bacteria break down waste materials. Farmers also use ammonia-based fertilizers to help crops grow, since plants need nitrogen to thrive. In fact, the invention of a process to make ammonia artificially in the early 1900s revolutionized farming by making fertilizer cheap and abundant, helping feed billions of people.

The word can also refer to the liquid form: ammonia water or household ammonia. When people say a place “smells like ammonia,” they usually mean it has that distinctive, harsh chemical odor that makes you want to back away quickly.