The adenoid is a kind of tonsil, a mass of tissue at the top of the place where the mouth meets the throat. In children it forms a soft mound just behind and above the other tonsils. In this way the adenoid and the tonsils provide a defensive ring against infection. Because it is similar to tonsils, when people have tonsils removed, they also sometimes have the adenoid removed as well.

The adenoid grows quite quickly in young children, and this may slightly block the airways, which is why some young children snore. But as children grow older their throats get larger and this is less and less of a problem.

An infected and enlarged adenoid can become nearly the size of a ping pong ball and completely block airflow. When this happens you can no longer breathe properly through your nose and you start to breathe through your mouth.