Polymorphous Light Eruption: A Sensitivity to Sunlight

It's not uncommon to break out in an unexplained rash. Most of these mysterious eruptions disappear as quickly as they appear. You may wonder whether it was something you ate, a new body lotion or a reaction to a new brand of washing powder. Few people consider that it may be a reaction to sunlight.

Polymorphous (or polymorphic) light eruption (PLE) is an inflammatory response to light that results in skin inflammation. It is more common in women and the fair-skinned. It is estimated that perhaps 10% of American suffer from the condition, whereas the incidence is as high as 20% of the population in Sweden. Though benign in most respects, it can cause considerable psychological distress.

Symptoms

The rash varies from person to person (polymorphous means 'many forms'), but typically manifests as numerous small, raised, itchy spots about a quarter of millimetre in diameter. Blisters and lesions are other possible forms. On the positive side, it rarely appears on the face and does not leave scars.

The rash may only appear a day or so after being in the sun, so many people don't make the connection with sunshine or sunbathing. The telling sign is that it appears on parts of the body that are not usually exposed to sunlight, often appearing at the beginning of a holiday.

Some people experience the rash in spring, or when abruptly exposed to the sun, but become desensitised with ongoing exposure. For an unlucky few, the condition may persist for years, cropping up with every excursion into the sun, and even increasing in severity year after year.

Though PLE is thought to be an immune response, the particulars of the condition are not fully understood. The specific external trigger is ultraviolet light (both UVA and UVB), which can penetrate clothing and is not filtered out by ordinary window glass. The fact that PLE more commonly affects women and that occurrence tails off in post-menopausal women, suggests a hormonal component. Fortunately, incomplete understanding of the condition does not mean that there is no treatment.

Prevention and treatment

Staying out of the sun altogether - bearing in mind that UV light penetrates through windows - is the obvious solution for sufferers from this photodermatosis. Slow, incremental exposure to the sun often helps 'harden' the sufferer. Those stricken with the problem on holiday may find that by the end of it their sensitivity has all but disappeared. If building up sun tolerance, the sun should be avoided during the middle of the day (11 a.m. - 3 p.m.) when radiation is more intense. Liberal applications of sunscreen (SPF 30 or even higher) are recommended, but sun creams don't necessarily help.

If you suspect that a rash is due to sun exposure, then you should stay out of the sun altogether while the rash is present to avoid exacerbating it. Though the condition does not leave scars, it can be extremely itchy and scratching can scar, even if the rash itself does not.

For the more seriously afflicted, steroid treatments or ultraviolet treatments prior to a holiday (or at the end of winter) may be recommended by your dermatologist. UV-resistant clothing is another option to consider in more extreme cases.

References:
Polymorphic light eruption. Dermnet NZ (New Zealand Dermatological Society). www.dermnetnz.org/reactions/pmle.html
Polymorphous light eruption. Emedicine. www.emedicine.com/DERM/topic342.htm