The tonsils are areas of lymphoid tissue on either side of the throat. An infection of the tonsils is called tonsillitis.

As with other organs of the lymphatic system, the tonsils act as part of the immune system to help protect against infection. In particular, they are believed to be involved in helping fight off pharyngeal and upper respiratory tract infections.

Tonsils in humans include, from superior to inferior: pharyngeal tonsils (also known as adenoids), tubal tonsils, palatine tonsils, and lingual tonsils. Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring. Tonsils tend to reach their largest size near puberty, and they gradually atrophy thereafter.

Most commonly, the term "tonsils" refers to the palatine tonsils that can be seen in the back of the throat.

Tonsillitis

Tonsillitis causes sore throat and fever. In chronic cases, or in acute cases where the palatine tonsils become so swollen that swallowing is impaired, a tonsillectomy can be performed to remove the tonsils. Patients whose tonsils have been removed are still protected from infection by the rest of their immune system.

When bacteria that collect on the tonsils consume mucus that has pooled in pits (referred to as "crypts") in the tonsils, a whitish-yellow deposit known as a tonsillolith is produced. These "tonsil stones" emit a very pungent odour due to the presence of volatile sulphur compounds.