A pox is a disease that causes spots, bumps, or sores to appear on the skin. The most famous example is chickenpox, which gives people itchy red spots all over their body. Another is smallpox, a deadly disease that once killed millions of people but was completely wiped out by vaccines in 1980, one of medicine's greatest victories.

Before modern medicine, pox diseases were common and dangerous. Today, vaccines protect us from many of them.

You might hear someone say “a pox on your house!” in old books or movies. This is an old-fashioned curse, like wishing bad luck on someone, though people rarely say it seriously anymore. It reflects how frightening these diseases once were, when having pox could mean weeks of misery or even death. Now, thanks to vaccination and medical advances, many pox diseases are preventable or much easier to treat.