A sanitizer is a substance that kills germs and bacteria on surfaces or skin to make them cleaner and safer. When you use hand sanitizer, you're putting a gel or liquid (usually containing alcohol) on your hands that destroys most of the invisible germs living there. Hospitals use powerful sanitizers to keep operating rooms sterile, and restaurants use sanitizers to clean tables and kitchen equipment between uses.

Sanitizing doesn't necessarily mean making something perfectly sterile (completely germ-free), but it reduces germs to safer levels. Hand sanitizer became especially common during the COVID-19 pandemic, when people used it frequently when soap and water weren't available.

You might also hear the verb form: a janitor sanitizes the bathroom, or a dentist sanitizes tools between patients. While washing with soap and water is usually the best way to clean your hands, sanitizer offers a convenient backup when you can't get to a sink, like after touching a grocery cart or before eating lunch at a picnic.