A true sun allergy—called solar urticaria—is very rare, affecting an estimated 0.5 percent of people. We’re not talking sunburns here! “Some 10 percent of the world’s population might have a skin reaction when exposed to the sun,” says dermatologist Gordon Searles, MD. These reactions can be broken down into two types: sun allergy and sun sensitivity.
“People with a sun allergy will break out in hives when exposed to the sun, in the same way that someone who is allergic to shellfish would break out in hives,” Dr. Searles says. The reaction is very quick. “A couple of minutes after someone [with a sun allergy] goes into the sunlight, they would develop a reaction,” he says. “The number one way to treat it is to avoid the sun.” But unlike some allergies, it is not life-threatening. “It’s uncomfortable.”
Sun sensitivity, on the other hand, is far more common. It’s characterized by little red itchy bumps or patches of redness like a rash, and the reaction is delayed. It doesn’t happen until later in the day or even the day after sun exposure, and it can look like an exaggerated sunburn, says Dr. Searles. While some sun sensitivities can be a side effect of certain medications (for example, some antibiotics cause a sensitivity called photodermatitis), the most common cause, says Searles, is called polymorphous light eruption, which is an internal immune system reaction to sun exposure.
Summer 2013 issue Best Health magazine