A lesion is any area of damaged or abnormally changed tissue in the body. When doctors examine a patient and find a lesion, they're looking at a spot where something has gone wrong: the tissue there doesn't look or work the way it should.

Lesions come in many forms. A cut on your skin is a lesion. So is a bruise, a scrape, or a patch of irritated skin from poison ivy. Inside the body, lesions might appear on organs or bones, discovered through X-rays or scans. A cavity in your tooth is a lesion where decay has damaged the enamel. An athlete might have a lesion on their knee cartilage from an injury.

The word simply describes damaged tissue without telling you what caused it or whether it's serious. Some lesions heal quickly on their own, like a scraped knee. Others need medical treatment. Doctors use lesion as a neutral, precise term when they're describing what they observe. For example, “I see a lesion on the lung” means they've found an area that looks different from the healthy tissue around it, and they'll need more information to understand what caused it and how to treat it.