How do smelling salts work?

Smelling salts work by releasing ammonia, which has a pungent and acrid odor that irritates the lining of the nose and lungs. This irritation causes a reflex that speeds up breathing and increases oxygen in the blood, which can quickly restore alertness.

Early smelling salts were made from ammonium carbonate mixed with perfume. Modern versions usually contain ammonia dissolved in water and ethanol, and sometimes infused with scents such as eucalyptus. References to ammonium salts go back to Roman and Arab scholarship, and by the 17th century chemists had developed ammonium carbonate for use in smelling salts. They became especially popular in the 18th century, often carried in decorative containers to revive individuals who had fainted.

Smelling salts can revive someone who has fainted, but they are not without risks. They can cause a brief rise in heart rate and breathing, similar to the body’s fight-or-flight response. Side effects can include chemical burns to the eyes, nose, or skin, as well as a whiplash effect from the sharp inhalation, which can injure the neck, back, or spine. People with such respiratory illnesses as asthma or bronchitis may also find that smelling salts worsen their symptoms. Overuse of smelling salts can harm the lungs and nasal passages.