Photodermatitis is a type of allergic contact dermatitis, which differs from other types of this condition, in that contact with the allergen does not cause symptoms until the skin is exposed to sunlight. Dermatitis simply means inflammation of the skin.

A red itchy rash is the usual symptom. The rash may resemble small blisters. The blisters and the surrounding area may peel. Nausea is sometimes experienced. In some cases, blotches of skin may be itchy for extended periods of time. The color of the skin may change as a result to an orange or brown color. Any part of the skin exposed to sunlight may be affected, depending on the triggering allergen.

What causes photodermatitis?

Chemicals, drugs, herbal remedies, plants, skincare products and the B-vitamin deficiency pellagra can be the underlying cause of photodermatitis. It is important to try to identify the cause in order to figure out treatment and prevention options.

Chemicals that often cause the reaction include salicylanilide and hexachlorophene. Salicylanilide is an ingredient commonly found in industrial cleansers. Hexachlorophene is found in some antibacterial soaps and cleansers.

Antibiotic drugs often cause increased sensitivity to sunlight. The drug’s label will usually bear a warning concerning this. Ibuprofen and other pain-relieving drugs can also cause the problem.

The herbal remedy St John’s wort, which is used in the treatment of depression in some countries, but sold over the counter in the U.S., is known to cause photo-sensitivity. Other herbs may have the same effect.

Many plants contain compounds that trigger the reaction. Common plant causes include parsnips, parsley, celery, hogweed, wild carrot, lemons, limes and figs.

Some ingredients found in skincare products are photo-sensitizers including PABA, benzoyl peroxide, retinoids, lemon oil, Psoralens, coal tars, methyl-coumarin and musk. PABA is a common sunscreen ingredient, which seems strange when it can cause photodermatitis. Benzoyl peroxide and retinoids are found in acne treatments and wrinkle creams. Lemon oil, methyl-coumarin and musk are fragrance ingredients. Psoralens and coal tars are primarily found in treatments for eczema and psoriasis.

What are the best treatment options?

Identifying the cause and avoiding it in the future works for prevention. The use of sunscreens free of PABA is recommended especially when the condition is caused by drug being used to treat a medical condition.

When a reaction occurs without warning, the affected area should be rinsed with cool water to provide relief and to remove the allergen. Calamine lotion may relieve the itch. Oral antihistamines such as Benadryl are useful, but should be taken only at nighttime, because of the drowsiness side effect.

Photodermatitis typically resolves quickly with minimal treatment, but the condition can become chronic if the allergen trigger is not identified and avoided.