Adenoids are masses of lymphatic tissue that help the body fight infection.
The adenoids are located in the pharynx, just behind the nose; along with the tonsils, they are the first line of defense against bacteria and viruses. Adenoiditis is inflammation of the adenoids caused by infection.
Adenoids are part of the lymphatic system, which plays several roles in protecting against infection: many white blood cells circulate there, reacting to potential pathogens that threaten the body.
If, during childhood, adenoids play an important role in keeping a person healthy, they become less and less useful as the years go by because the body is able to fight the infection in other ways. In fact, adenoids often become smaller around the age of five or six and practically disappear by the time they reach adolescence.