In medicine, sensitivity may describe how well a test can detect a specific disease or condition in people who actually have the disease or condition. No test has 100% sensitivity because some people who have the disease or condition will not be identified by the test (false-negative test result). Sensitivity may also refer to the way the body reacts to the environment or to drugs, chemicals, or other substances. For example, a person who is sensitive to the sun may have skin that burns easily or get a rash when exposed to the sun. A person who is sensitive to caffeine may need only small amounts of it to feel its effects.