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Too much ultraviolet light causes irritating sun rashes

Why do sun rashes happen? Do they increase with age? Is there anything we can do to prevent them?

Dolores S., Medford

These rashes are caused or exacerbated by exposure to the sun, so it's no surprise they are most commonly seen during the summer, says Dr. David Trask a Medford dermatologist.

Trask says a number of things can cause sun rashes, and the list includes such unlikely stuff as antibiotics and the juice of limes and figs. Even sunscreens that are sold to protect the skin from excessive sun can cause a rash in some people.

Trask says people with fair complexions are most vulnerable to these rashes. There are a number of different kinds of rashes, and physicians have names for all of them. Generally, age has nothing to do with whether we get them, or how frequently they occur.

In the most common type ("polymorphous light eruption") red bumps and blisters develop on skin that has been exposed to the sun. Trask says this rash often develops at the beginning of summer, gradually improves as the season wears on, and may recur the following summer. It can run in families, and it tends to affect men and women about equally.

Physicians believe the rash develops when the immune system reacts to too much ultraviolet light, but the exact mechanism has not been explained. These rashes can usually be avoided by preventing exposure to sunshine, either by applying sunscreen to exposed skin or wearing protective clothing.

Another type of sun rash is caused by a reaction to medicine. Many commonly-used medicines can cause these "phototoxic" rashes, which are characterized by a sunburn-like rash on areas of the skin that have been exposed to the sun.

Many well-known medicines produce these "phototoxic" rashes, including antibiotics such as Cipro and the tetracyclines, nonsteroidal anti-inflammatories such as Naprosyn and Aleve, and Accutane, which is used for severe cases of acne.

Trask says the amount of sun exposure required for this rash to develop depends on the skin type and the amount of skin exposed. These rashes usually can be avoided by staying indoors while taking medicines that make the skin more sensitive to the sun, or by severely limiting exposure to the sun.

There are also "photoallergic" sun rashes that occur when an oral medication or some other substance applied to the skin causes an allergic reaction to develop in the presence of ultraviolet light.

Ironically, in the United States, the most common cause of these reactions is sunscreen, Trask says. Applying these lotions and creams can trigger an itchy, red blistery eruption on sun-exposed skin. Certain fragrances in creams and lotions also can trigger an allergic reaction, along with antibacterial agents such as hexachlorophene.

Trask says avoiding these products if they cause a rash is the best way to prevent them. A laboratory test can usually determine whether a product is the source of the reaction.

Exposing the skin to certain plant materials can also cause sun rashes. "Phytophotodermatitis" has been caused by parsley, celery, parsnips, lime, lemon and figs. Trask says grocery workers, among others, are prone to these patchy, red blistery eruptions. So are people who enjoy gin and tonics or other drinks that include a generous splash of lime juice.

"Lying on the beach while enjoying certain kinds of drinks is a relatively common cause of this sun-related problem," he said.

There are also "photo-aggravated dermatoses," internal or skin conditions that are worsened by exposure to sunlight. Systemic lupus, for example, is aggravated by sun exposure. Lymphoma can be associated with photo-aggravated dermatitis, and conditions such as acne, eczema, rosacea, and seborrhea can all be aggravated by exposure to the sun.

In general, clothing that blocks ultraviolet rays helps prevent these rashes, along with sunscreens that have broad protection against ultraviolet A and B. People who have oily skin will find alcohol-based gels less likely to cause skin problems. For people with dry skin, creams are generally easier to use.

Trask says a new sunscreen marketed by L'Oreal under the brand name Anthelios SX contains a new sunscreen, Mexoryl SX, which should provide good protection when it becomes available (probably later this fall). Sunscreens with an SPF rating of 30 or more should be used for the best protection.

Call Bill Kettler with your medical questions at 776-4492, or e-mail them to: bkettler@mailtribune.com or send them to: Mail Tribune, Ask Your Doctors, P.O. Box 1108, Medford OR 97501.