Sensitivity of the skin to ultraviolet light, resulting in redness and discomfort
Photosensitivity is defined as an abnormal reaction of the skin to the effects of ultraviolet rays in sunlight. The condition is sometimes present at birth and sometimes develops later in life.
Various substances may cause photosensitivity, including drugs such as tetracyclines (see Antibiotics), diuretics, and, rarely, oral contraceptives. Photo-sensitivity may also result from the use of certain cosmetics. The condition sometimes occurs in people who have systemic lupus erythematosus, or porphyria. When there is no obvious cause, the condition is referred to as primary photosensitivity.
The reaction occurs in areas frequently exposed to sunlight. It usually develops shortly after exposure but may be delayed for 24–48 hours. The symptoms include:
Red, often painful rash.
Small, itchy blisters.
At a later stage, the nails may lift from the nail beds. Sometimes, affected people also develop generalized redness on all exposed skin. In rare cases, people with severe photosensitivity are unable to go outdoors in daylight.
Your doctor will probably make a diagnosis from the appearance of the rash. If the reaction is thought to be caused by a drug, the doctor may prescribe an alternative. You may also need blood and urine tests to check for under-lying disorders.
To relieve the symptoms, you may need to use a topical corticosteroid or oral antihistamine (see Antipruritic drugs). Severe cases are treated with controlled exposure to ultraviolet light, sometimes combined with drugs, to desensitize the skin.
You can help control the reaction by avoiding sunlight as much as possible. When outdoors, cover your skin, wear a hat, and use a high-factor sunblock.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.