The adenoids (say: ADD-eh-noids) are a patch of tissue that protects kids from getting sick. They sit in the back of the nasal cavity. Although you can easily see your tonsils by standing in front of a mirror and opening your mouth wide, you can't see your adenoids this way. Like tonsils, adenoids help keep your body healthy by trapping harmful bacteria and viruses that you breathe in or swallow.

Adenoids do important work as infection fighters for babies and little kids. But they become less important once a kid gets older and the body develops other ways to fight germs. Adenoids usually shrink after about age 5, and by the teenage years they often practically disappear.

Because adenoids trap germs that enter the body, adenoid tissue sometimes temporarily swells (gets puffier) as it tries to fight off an infection. The swelling sometimes gets better, but sometimes adenoids can get infected themselves.