Section 18. Skin Disorders

Chapter 214. Sunlight and Skin Damage

Topics: Introduction | Sunburn | Skin Photosensitivity Reactions

Skin Photosensitivity Reactions

Photosensitivity, sometimes referred to as a sun allergy, is an immune system reaction that is triggered by sunlight. Photosensitivity reactions include solar urticaria, chemical photosensitization, and polymorphous light eruption and are usually characterized by an itchy eruption on patches of sun-exposed skin. People may inherit a tendency to these reactions. Certain diseases, such as systemic lupus erythematosus and some porphyrias, also may cause the skin to break out in response to sunlight.

Solar urticaria are hives (large, itchy red bumps) that develop after only a few minutes of exposure to sunlight. The hives appear within 10 minutes of sun exposure and go away within an hour or two after leaving the sunlight. People with large affected areas often have headaches and feel weak and nauseated.

Chemical photosensitivity is a condition in which people develop redness, inflammation, and sometimes brown or blue discoloration in areas of skin that have been exposed to sunlight for a brief period. This reaction differs from sunburn in that it occurs only after the person has swallowed certain drugs or chemicals or has applied them to the skin. These substances make some people's skin more sensitive to the effects of ultraviolet light. Some people develop hives with itching, which indicates a type of drug allergy that is triggered by sunlight.

Polymorphous light eruption is an unusual reaction to sunlight, the cause of which is not understood. It is one of the most common sun-related skin problems and is more common in women and in people who are not regularly exposed to the sun. The eruption appears as multiple red bumps and irregular red patches appearing on sun-exposed skin. These patches, which are itchy, generally appear between 30 minutes and several hours after sun exposure; however, new patches may develop many hours or several days later. The bumps and patches usually go away within a week. Typically, people with this condition who continue to go out in the sun gradually become less sensitive to the effects of sunlight.

See the sidebar Some Substances That Sensitize the Skin to Sunlight.

Diagnosis, Prevention, and Treatment

There are no specific tests for photosensitivity reactions. A doctor suspects a photosensitivity reaction when a rash appears only in areas exposed to sunlight. A close review of any diseases, drugs taken by mouth, or substances applied to the skin (such as drugs or cosmetics) may help a doctor pinpoint the cause of the photosensitivity reaction. Doctors may perform tests to rule out diseases, such as systemic lupus erythematosus, that are known to make someone susceptible to such reactions.

A person with sensitivity to sunlight from any cause should wear protective clothes, avoid sunlight as much as possible, and use sunscreens. If possible, any drugs or chemicals that could cause photosensitivity should be discontinued.

People with polymorphous light eruption or lupus photosensitivity sometimes benefit from treatment with hydroxychloroquine or corticosteroids taken by mouth. For certain types of photosensitivity, treatment can consist of phototherapy (exposure to ultraviolet light) with the use of psoralens (drugs that sensitize the skin to the effects of ultraviolet light). This treatment is called PUVA (psoralens plus ultraviolet A (see Section 18, Chapter 203)). However, people with systemic lupus erythematosus cannot tolerate PUVA therapy.