What is Polymorphic Light Eruption (Sunlight Sensitivity)?
Polymorphic light eruption is a type of skin condition that reacts to sunlight, making it the most common light-induced skin reaction triggered by the immune system. When people with this condition are exposed to sunlight, especially in the spring or summer, they may develop an uncomfortable skin rash. However, this rash usually goes away in a few days if they stay out of the sun. There are varying forms of this condition; one form, known as juvenile spring eruption, affects young boys, causing blister-like spots on their ears. Another form, PMLE sine eruption, leads to itchiness on skin exposed to sunlight without any visible changes to the skin. Polymorphic light eruption can also be referred to as polymorphous light eruption or prurigo aestivalis.
What Causes Polymorphic Light Eruption (Sunlight Sensitivity)?
The reason behind polymorphic light eruption, a skin condition caused by reaction to sunlight or artificial ultraviolet (UV) light, is still not fully understood. It is thought to be a delayed allergic reaction to a natural substance in the body that becomes noticeable after exposure to sunlight or artificial UV light. This theory also has to explain why the condition is more common in women and why continuous exposure to UV light seems to make the condition less severe.
Risk Factors and Frequency for Polymorphic Light Eruption (Sunlight Sensitivity)
Polymorphic light eruption is a condition that varies in prevalence around the world. Sufferers might experience this condition every time they go outside, or only from time to time. It’s more commonly found in Northern Europe, specifically in around 15% of the UK population, than in Australasia, where it affects around 5% of the population.
- This condition can impact people of all skin types, but is more commonly seen in lighter skins, especially those with Fitzpatrick skin phototype 1.
- About 75% of the time, it starts in females between the ages of 20 and 40, but it can also start in childhood or later in life.
- Interestingly, more people experience this condition at high altitudes than at sea level.
Signs and Symptoms of Polymorphic Light Eruption (Sunlight Sensitivity)
Polymorphous light eruption is a condition that typically begins after intense sunlight exposure, especially during the spring or early summer in temperate climates. Some people only develop this condition after being exposed to light therapy for other skin inflammation conditions. The first sign is a rash that appears on parts of the body that have recently been exposed to sunlight – including the lower legs, backs of hands, forearms, and upper chest. It rarely affects the face.
The rash can take on many forms, which can vary from person to person. The most common is a red bump-like rash that can sometimes merge to form larger skin patches. Other possible types include flat skin discolorations, blisters, plaques similar to skin lichen, itch-inducing bumps, and ring-like lesions that can look like another skin condition called erythema multiforme.
While quite rare, some people might experience symptoms beyond the skin, such as fever, fatigue, and headaches.
Generally, the rash goes away on its own after several days, as long as one avoids additional UV exposure. However, continuing exposure can cause the rash to last for weeks or even months. The good news is that most people become less susceptible to the rash after gradual sun exposure over the season, making the condition less likely to occur in the late summer.
This condition usually comes back every year and, for some people, might persist throughout the year depending on how close they live to the equator. However, the severity often lessens over time and becomes less common as people get older.
Testing for Polymorphic Light Eruption (Sunlight Sensitivity)
If you undergo a skin biopsy due to suspicion of a condition called polymorphic light eruption (a type of skin rash), the test might reveal swelling in the upper layer of the skin and a heavy concentration of certain immune cells around blood vessels and sweat glands. These immune cells consist of two types: plasmacytoid dendritic cells and T regulatory cells. Early-stage skin lesions might also contain a type of white blood cell called neutrophils. Depending on your symptoms, the skin biopsy may show certain characteristic changes such as spongiosis (swelling of skin cells), the formation of blisters, or the breakdown of skin cells. However, a test called direct immunofluorescence, used to detect certain skin diseases, will be negative.
Polymorphic light eruption doesn’t usually alter your blood test results. But in some cases, tests may show the presence of specific proteins (antibodies) that attack cell nuclei. These proteins, called antinuclear antibody and extractable nuclear antigen, can sometimes be found even if you don’t have any other symptoms of a related disease called lupus. If your symptoms or medical history suggest it, your doctor may test your urine and red blood cells to rule out other diseases, but these tests usually come back negative.
Photo testing, a test which measures your skin’s reaction to ultraviolet light, is not often needed. Some specialized centers may perform this test, called photoprovocation, in late winter to learn which types of light trigger the rash. This method exposes small areas of your skin to varying doses of ultraviolet light for three days, and then checks for the typical rash. However, the test may not always produce accurate results, giving false negatives in 10% to 40% of individuals tested. Another test known as formal monochromator MED testing checks your skin’s sensitivity to different wavelengths of light, but it typically gives normal results based on your skin color.
Treatment Options for Polymorphic Light Eruption (Sunlight Sensitivity)
The best way to manage the skin eruption is by figuring out what causes it and then trying to avoid this trigger as much as possible. It’s also helpful to slowly increase exposure to the trigger to build up your body’s resistance.
It’s important to understand that UV-A rays, which are a large part of sunlight, can cause a skin eruption without causing a sunburn. This is because sunburn is mainly caused by UV-B rays. UV-A rays can pass through window glass and aren’t fully blocked by sunscreens. Hence, when you’re in conditions that might cause a rash, try to cover as much of your skin as possible with clothing made from tightly woven fabric.
Choose a sunscreen that protects against a wide range of sunlight, is water-resistant, and is semi-opaque, with a sun protection factor (SPF) of 50+. It’s a good idea to apply this sunscreen before you go outside and then every two hours on any skin that’s not covered by clothing.
Starting in the late winter or early spring, you can help to lower the chance and severity of a polymorphous light eruption by getting low doses of narrowband UV-B and other types of phototherapy. This typically involves 2 to 3 treatments a week for 4 to 6 weeks each year.
There’s also some evidence that taking short courses of oral steroids can help to prevent a skin eruption. Other possible prophylactic (preventive) treatments include hydroxychloroquine and antioxidants such as Polypodium leucotomes extract, lycopene, beta-carotene, nicotinamide, and astaxanthin.
If you do have a skin eruption, it can be treated with topical corticosteroids, which are creams or ointments that you apply to your skin. These can help to lessen the symptoms and shorten the duration of the rash.
What else can Polymorphic Light Eruption (Sunlight Sensitivity) be?
The primary condition doctors might mistake for photosensitivity is lupus erythematosus. Although it has a similar appearance and behavior, lupus tends to last longer. Another condition to consider is solar urticaria, which can occur soon after sun exposure and usually clears up within an hour or so of covering up. Photosensitivity dermatitis is a more stubborn condition with symptoms resembling eczema.
Possible Complications When Diagnosed with Polymorphic Light Eruption (Sunlight Sensitivity)
While polymorphous light eruption usually doesn’t lead to severe problems, if it does become serious, it can cause emotional stress, anxiety, and depression.
