To desensitize means to make someone less sensitive or responsive to something, usually through repeated exposure. When you first hear a loud noise, you might jump or feel startled, but if you hear that same noise over and over, you gradually stop reacting to it. Your nervous system has become desensitized.

Doctors sometimes desensitize patients who have severe allergies by giving them tiny amounts of the allergen over time, gradually training their bodies not to overreact. A person afraid of dogs might slowly desensitize themselves by first looking at pictures of dogs, then watching dogs from a distance, then eventually being near calm, friendly dogs.

The word often comes up when people worry about becoming desensitized to violence or disturbing content through movies, video games, or news. The concern is that seeing upsetting things repeatedly might make someone care less about them or react less strongly to real suffering. Whether playing a video game actually desensitizes someone to real violence remains debated by researchers.

You can also desensitize your skin: if you've ever had a cavity filled at the dentist, the dentist probably used medicine to desensitize your gums so you wouldn't feel pain during the procedure.