Although die-hard sun worshipers continue to oil up to better catch the sun's tanning rays, most Americans choose to slather on sunscreen instead. Sunscreen can help protect them from most of the harmful effects of ultraviolet light, but it will do little for certain sun-sensitive individuals. These would-be sun seekers wind up with an itchy, bumpy rash that is sometimes called "sun poisoning" even if they're wearing SPF 50. "Sun poisoning" is really an allergic reaction to the sun that occurs when skin is exposed to sunlight for the first time in the early spring, or during a winter vacation. While people with light skin are most susceptible to sunburn, sun allergy affects people of all skin colors. If people with sun allergy venture to the beach at all, you can probably find them in a floppy hat, under an umbrella. Or, at least, that's where they should be. Below, Henry W. Lim, MD, chair of the department of dermatology at Henry Ford Hospital in Detroit, Michigan, talks about how to prevent and treat allergic reactions to the sun, as well as rashes triggered by sunscreen ingredients. Can someone have a sun allergy? There are certain skin reactions to the sun that have nothing to do with sunscreen or other external factors, which we call an intrinsic type of photodermatosis. People with photodermatosis develop skin rashes following exposure to the sun. Polymorphous light eruption is the most common type of photodermatosis. It is most likely due to an abnormal immune system reaction to the sun. Polymorphous light eruption occurs in approximately 10 to 20 percent of otherwise healthy individuals, so it is a relatively common condition. Then there is another group of people who develop what they think is a sun allergy because of medications that they have ingested or agents that they have applied, including sunscreen. These people develop an irritant reaction, which is a rash or a tingling, itchy sensation on the skin. The chances of getting a true allergic reaction to sunscreen are actually very low. What are the symptoms? People usually develop reactions within a few hours of sun exposure. The typical scenario would be that they get exposed to the sun during the day, and then at the end of the day they start noticing the development of red bumps or blisters in the exposed area. It tends to be somewhat itchy. The polymorphous light eruption produces a rash that looks more like hives or insect bites. Sometimes people have no symptoms. If the reaction is untreated, it usually lasts for a few days, or up to two weeks. Then it would go away by itself. Does it get worse or better with repeated exposure? It tends to occur most commonly in the springtime in a temperate climate when people first start getting sun exposure. Typically as the season progresses, the person becomes less sensitive to developing this reaction; the thought is that the skin adjusts to this effect of the sun. But any kind of sudden and relatively intense exposure to the sun would bring this up. A typical scenario in the winter is when patients from Northern climates go to the Caribbean or Hawaii, for example, for their winter vacation. Can someone develop sun allergy at any time in their life? It can occur at any time in someone's life, but typically it occurs in people in their 20s and their 30s. And it can occur in people of all skin types. So not only Caucasians, but also Asians, Latinos and black people can develop photosensitivity. Is sun allergy ever a sign of an underlying condition? There have been some reports of an association with lupus and with thyroid problems, but those are exceptions rather than the rule. We do evaluate patients for those conditions on a routine basis. We ask them questions and take some blood tests, if necessary. But the vast majority of patients are perfectly healthy otherwise. What kind of ultraviolet light causes the reaction? It's usually UVB light, but it could be UVA also. So it varies from person to person and one would have to test for it. The testing is usually conducted in a clinic setting. We can use light sources that emit predominantly UVB or light sources that emit predominantly UVA to see which one would induce the lesion. That would help to guide the treatment somewhat. Realistically, however, the testing is not that widely available because only specialized photodermatology centers would be able to perform it, and it is not 100 percent positive in all patients. What medications might increase risk of sun allergy? There's a whole long list of oral medications that can make skin more sensitive to sunlight. This includes some forms of antibiotics such as tetracyclines. Certain diuretics, or water pills, also frequently make the skin more sun-sensitive. My suggestion usually is that if people have sun allergies, they ask their primary care physician about their medications' side effects. How are allergic reactions to the sun treated? Beyond staying in the shade, wearing protective clothing and using sunscreen, we recommend topical corticosteroids to treat the rash. Some are over-the-counter, such as hydrocortisone, but that's not very potent. The more severe reactions require a prescription cortisone cream or ointment. For very severe reactions, we have to use oral cortisone to bring down the inflammation. If we know that someone has polymorphous light eruption every summer, we may give them ultraviolet light treatment as a way to desensitize the skin in the spring. It's almost like you're going to an allergist for allergy shots. By exposing your skin to ultraviolet light, your system gets used to it. Usually we do about 15 treatments. The second approach to treat a rash is to use a medication called Plaquenil (hydroxychloroquine), which is an antimalarial agent that has been used for various skin conditions; it works quite well for polymorphous light eruption. How can people avoid allergic reactions to the sun? As a first-line treatment, we usually ask the person to avoid the sun if possible, and if they do go out in the sun to use photo-protective measures. So in addition to staying in the shade, they should wear a long-sleeve shirt if possible and use what we call broad-spectrum sunscreen that has UVB as well as UVA blockers. If someone knows that they are only sensitive to UVB, it's not as essential that they use the broad-spectrum sunscreen. We ask people to look for sunscreen that has SPF 15 or above because the probability of having UVB and fairly good UVA protection is quite good. People should specifically look for the word "broad-spectrum" on the label. How can people avoid sunscreen reactions? If the reaction is due to irritation secondary to an ingredient in the sunscreen, clearly an avoidance of that ingredient is the first step. Usually I tell the person to try different types of sunscreens. A lot of the time sunscreens for children or sunscreens for the face tend to be better tolerated because they have less alcohol content, so sometimes I recommend trying those. Another approach is using sunscreen that contains only titanium dioxide and zinc oxide. Those two ingredients have never been reported to cause allergic reactions. When should you see a dermatologist or a doctor if you think that you might have a sun allergy? I think if you have more than one episode, or if you have a very severe episode of skin eruption following sun exposure, it would be worthwhile to consult a dermatologist at that time. You might also see a dermatologist if your first-time reaction doesn't go away after a few days, or if it's very itchy, very red, very bumpy, very extensive. If untreated, the area will continue to be uncomfortable and could lead to an infection or skin breakdown.