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• Sunlight can trigger immune reactions.
• People develop itchy eruptions or areas of redness and inflammation on patches of sun-exposed skin.
• These reactions typically resolve on their own.

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: Hives (large, itchy red bumps) that develop after only a few minutes of exposure to sunlight are called solar urticaria. The hives appear within 10 minutes of sun exposure and generally last for only a few hours. A person can be prone to developing solar urticaria for a very long time, sometimes indefinitely. People with large affected areas sometimes have headaches and feel dizzy, weak, and nauseated.

Chemical Photosensitivity: In chemical photosensitivity, 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 taken certain drugs (such astetracycline

) or chemicals or has applied them to the skin (such as perfume or aftershave). These substances make some people's skin more sensitive to the effects of ultraviolet (UV) light. Some people develop hives with itching, which indicates a type of drug allergy that is triggered by sunlight.

Polymorphous Light Eruption: This 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 most common among women and among people from northern climates who are not regularly exposed to the sun. The eruption appears as multiple red bumps and irregular red patches 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 several days to a week. Typically, people with this condition who continue to go out in the sun gradually become less sensitive to the effects of sunlight.

Some Substances That Sensitize the Skin to Sunlight Antianxiety drugs Alprazolam Chlordiazepoxide Antibiotics Quinolones Sulfonamides Tetracyclines Trimethoprim Antidepressants Tricyclic antidepressants Antifungal drugs (taken by mouth) Griseofulvin Antihyperglycemics Sulfonylureas Antimalarial drugs Chloroquine Quinine Antipsychotics Phenothiazines Diuretics Furosemide Thiazides Chemotherapy drugs Dacarbazine Fluorouracil Methotrexate Vinblastine Drugs used to treat acne (taken by mouth) Isotretinoin Heart drugs Amiodarone Quinidine Skin preparations Antibacterials ( chlorhexidine ,hexachlorophene ) Antifungal drugs Coal tar Fragrances Sunscreens

Diagnosis

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.

Prevention and Treatment

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 after consulting with a doctor.

People with polymorphous light eruption or lupus photosensitivity sometimes benefit from treatment with corticosteroids applied to the skin or hydroxychloroquine

or corticosteroids taken by mouth. Occasionally, people can be desensitized to the effects of sunlight by gradually increasing their exposure to UV light.