A rash is a change of the skin that affects its color, appearance or texture. A rash may be localized to one part of the body or affect the skin entirely. Rashes may cause the skin to change color, itch, or become warm, bumpy, dry, cracked or blistered. Rashes can also swell and may be painful. The causes and treatments for rashes vary widely. Common causes include allergy, infection, irritation, medication, sun exposure, occupational exposure and insect bites.