"Photo" refers to light. A photosensitivity reaction is a disorder in which your immune system overreacts to sunlight. This reaction is sometimes also called a sun allergy.
Photosensitivity causes red, itchy patches on your skin, usually skin that has been in sunlight
Certain medicines or chemicals can make your skin sensitive to the sun
Photosensitivity reactions can run in families
Some diseases can cause a severe photosensitivity reaction
Photosensitivity reactions go away on their own, but medicine sometimes helps you feel better
There are different types of photosensitivity reactions that have different causes, including:
Those caused by certain medicines you take
Those caused by certain chemicals you were exposed to
Those caused by diseases you have (such as lupus)
At least 100 medicines and chemicals are known to cause photosensitivity.
Sometimes there doesn't seem to be a particular cause, although photosensitivity sometimes runs in families.
Symptoms are different depending on the type of photosensitivity reaction you have. You may have:
Symptoms usually appear only on skin that was exposed to the sun. But one kind of photosensitivity reaction can spread to skin that wasn't exposed to sun.
Doctors suspect a photosensitivity reaction when you have a rash mostly on areas of your skin exposed to the sun. Doctors will ask you about medicines and substances you take or apply to your skin.
Doctors may do tests, such as:
Your treatment depends on which type of photosensitivity reaction you have.
Doctors may also have you: