Exposure to sunlight

People who are allergic to the sun have to slather sunblock on exposed skin and reapply the lotion throughout the day.
People who are allergic to the sun have to slather sunblock on exposed skin and reapply the lotion throughout the day.PHOTO: ISTOCKPHOTO

Call them real-life vampires but there are some people who dread daylight. A brief exposure to sunshine can trigger an itchy rash or worse.

It is because they are allergic to sunlight and often have to slather sunblock on exposed skin, such as the forearms. They have to reapply the lotion throughout the day.

Sun allergy is an immune reaction in the skin which affects sun- exposed skin such as that on the forearms and lower legs.

About 10 to 20 per cent of a population have this affliction, said Dr Elizabeth Tham, an associate consultant at the division of paediatric allergy, immunology and rheumatology at National University Hospital. They may have one of several variants of this allergy:

•Polymorphous light eruption: An itchy skin rash which occurs within hours to a day of sun exposure. It is more common in females and occurs mostly in the first three decades of life. It usually subsides within a few days if the person avoids further sun exposure. Sunscreen and topical steroid creams can help.

•Photoallergic eruption: A skin rash triggered by sun exposure to a chemical applied to the skin. This chemical can be found in fragrances, cosmetics or sunscreen; or in oral medications like antibiotics, diuretics and contraceptives. The reaction tends to show up a few days after sun exposure. The person should stop using the product with the chemical. Doctors may also prescribe topical steroid creams.

• Solar urticaria: A rare condition that manifests as hives within a few minutes after exposure to sun or an artificial light source, most commonly in young women. The symptoms fade within a few hours but may recur on further sun exposure. The affected person is usually given oral antihistamines or topical steroids for more severe hives or, in extreme cases, phototherapy or anti-IgE treatment.

Dr Chong Yong Yeow, a specialist in rheumatology and consultant at Raffles Internal Medicine Centre, said he has had a few patients with connective tissue diseases such as lupus. They had sensitive skin, mainly on the shoulder areas (sun- exposed areas) and chest wall.

"The skin is red and itchy, but can be painful and have a rough surface," he said. "Often, we have to differentiate between a rash due to lupus and the intake of certain medicines, which can predispose patients to sunlight sensitivity."

Joyce Teo

A version of this article appeared in the print edition of The Straits Times on September 05, 2017, with the headline 'Exposure to sunlight'. Print Edition | Subscribe