What is sun allergy (polymorphic light eruption)?
The official name for sun allergy is polymorphic light eruption (PMLE). It is the most common form of light hypersensitivity. We only speak of sun allergy or light hypersensitivity when someone develops a skin inflammation after a normal exposure to light. PMLE is a fairly common condition.
Who gets it?
PMLE occurs equally in men and women. It arises more often in people with a fair skin type, but people of any skin colour can develop it. PMLE usually begins in young adulthood.
How does it develop?
Polymorphic light eruption is caused by light. Sunlight consists of visible light and invisible ultraviolet light; UV light is divided into (short-wave) UVB and (long-wave) UVA. UV light is responsible for tanning and sunburn — the normal skin reactions to ultraviolet light. In PMLE there are abnormal reactions to ultraviolet, and UVA is now regarded as the most important cause. Exactly why PMLE develops is unfortunately not yet known. It is clear, however, that people with fair skin who burn easily develop PMLE sooner than people with a darker skin type. It can begin at any age, even when someone previously tolerated sunlight well.
What does it look like?
The skin changes of PMLE usually appear 24 to 48 hours after exposure to sunlight, and sometimes it takes a few days longer. The most common are itchy patches on the light-exposed skin. Besides red papules, blisters, swelling (oedema) and scaling are also seen. Initially the changes are limited to light-exposed skin, but the reactions can spread to areas not exposed to light.
How is the diagnosis made?
Often the correct diagnosis can already be made from the course of the complaints. To find out whether the PMLE is caused by UVA or UVB, a dermatologist can carry out light tests. It can also often be worked out from your account: if the problems also arise behind glass, despite good sun-protection products, or in cloudy weather, UVA is the most likely cause.
How is sun allergy treated?
Light hardening (getting used to the sun). For most forms of sun allergy it is enough to let the skin gradually get used to sunlight in spring. Through this slow adaptation the skin thickens a little and produces pigment, giving protection against UV light. In spring (March/April), daily sun exposure can then be extended, taking more care on sunny days than on cloudy ones.
Light treatment in hospital. Depending on the type of PMLE (UVA- or UVB-caused) and its severity, “hardening courses” can be given at the dermatology clinic, in which the skin is exposed to a UV light source a few weeks each spring, 2 to 3 times a week.
Sunscreen. Sunscreens protect only to a certain extent, because most creams protect only against UVB while most forms of sun allergy are caused by UVA. A physical sunblock is therefore a better choice, although even that cannot be guaranteed to block all UVA, so caution is always needed.
Medicines. In exceptional cases PMLE can be treated with medicines belonging to the group also prescribed against malaria (although PMLE has nothing to do with malaria).
How do I prevent an outbreak of PMLE?
- Getting used to the sun in spring reduces the risk of (severe) attacks.
- The usual sun-protection measures are extra important for people with PMLE and should be applied even more strictly.
- Avoid sudden exposure to strong sun (for example on winter-sports holidays).
What is the outlook?
In most patients the complaints begin in (early) spring. With repeated exposure to light, the frequency of attacks decreases strongly over the summer and disappears completely in autumn and winter; the next spring the whole cycle begins again. The intensity can vary from year to year. Fortunately, in most people PMLE disappears on its own after a number of years.
When to see a doctor
See a doctor if you develop an itchy rash on sun-exposed skin in spring or summer, if it is severe or recurring, or for advice on light tests and prevention.