Nitric oxide is a colorless gas that is produced by virtually every cell in the body. It is a free radical, which means it has an unpaired electron, that plays an important role in the normal functioning of the body’s cells. It also regulates larger functions such as the nervous and immune systems.

It’s easy to confuse nitric oxide with nitrous oxide — but the two are very different.

Nitric oxide consists of one molecule of nitrogen and one of oxygen. Nitrous oxide has two molecules of nitrogen and one of oxygen. That extra molecule changes the gas completely.

Nitrous oxide — sometimes called “laughing gas” — is used as an inhalable anesthetic, often by dentists. It does not have the same cardiovascular benefits as nitric oxide.

But nitric oxide is a relatively newly discovered molecule — it was identified only about 40 years ago, and its health effects were later deemed so important the three scientists received the 1998 Nobel Prize in Physiology or Medicine for describing them.