Polymorphic light eruption is a fairly common skin rash triggered by exposure to sunlight or artificial ultraviolet (UV) light.
An itchy or burning rash appears within hours, or up to two to three days after exposure to sunlight. It lasts for up to two weeks, healing without scarring.
The rash usually appears on the parts of the skin exposed to sunlight – typically the head and neck, chest and arms (the face isn’t always affected).
Polymorphic light eruption is thought to be caused by UV light altering a substance in the skin, which the immune system then reacts to, resulting in the skin becoming inflamed.