An irritant is something that bothers, annoys, or causes discomfort. The word often describes physical things that make your body react uncomfortably: dust can be an irritant to your eyes, making them water and itch. Certain soaps might act as irritants to sensitive skin, causing redness or a rash. Pollen is a common irritant during spring, triggering sneezes and itchy noses for people with allergies.

The word also describes anything that persistently annoys or frustrates you. A squeaky desk chair that won't stop creaking might become an irritant during quiet reading time. A little brother who keeps tapping his pencil during homework could be a major irritant. Background noise from construction outside your classroom window can be a constant irritant, making it hard to concentrate.

Notice that irritants don't usually cause serious harm; they're bothersome rather than dangerous. A small paper cut can be irritating, but it is not usually an injury that requires a hospital visit. An irritant is that persistent, nagging thing that gets under your skin and won't let you forget it's there. The related verb is irritate, meaning to cause irritation or annoyance.