Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link
Quick Facts

Photosensitivity Reactions


The Manual's Editorial Staff

Last full review/revision Feb 2020| Content last modified Feb 2020
Click here for the Professional Version
Get the full details

What is a photosensitivity reaction?

"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

What causes photosensitivity reactions?

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.

What are the symptoms of a photosensitivity reaction?

Symptoms are different depending on the type of photosensitivity reaction you have. You may have:

  • Itchy, red swellings or bumps

  • Painful, red patches like sunburn

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.

How do doctors tell if I have a photosensitivity reaction?

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:

  • Skin patch tests to see what substances you may be allergic to

  • Shining a UV light on your skin to see if it causes the reaction

How do doctors treat photosensitivity reactions?

Your treatment depends on which type of photosensitivity reaction you have.

Doctors will:

  • Tell you to stop using any medicines or substances that cause photosensitivity

  • Give you corticosteroids to apply to your skin or take by mouth

  • Give you other medicines if the reactions are frequent or severe

Doctors may also have you:

  • Avoid spending too much time in sunlight

  • Wear protective clothing when you go outside

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version


Others also read

Test your knowledge

Abortion is defined as the intentional ending of a pregnancy by surgery or drugs. Which of the following statements about abortion in the United States is most accurate? 
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID