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Polymorphic light eruption

Polymorphic light eruption is a common rash that occurs as a result of photosensitivity.

Polymorphic light eruption (PMLE) generally occurs in adult females aged 20 to 40, although it sometimes affects children and rarely males. It is more common in places where sun exposure is uncommon, such as Northern Europe, where it is said to affect 10% of women holidaying in the Mediterranean. It can be the first sign of lupus erythematosus, but this is not usually the case.

The name ‘polymorphic’, or ‘polymorphous’ refers to the fact that the rash can take many forms, although in one individual it usually looks the same every time it appears.

The commonest variety is crops of 2-5 mm pink or red raised spots occurring on the arms. Other areas may be involved, particularly the chest and lower legs, but the face is usually spared.

Sometimes the rash looks like dermatitis, i.e. it is blistered and then larger dry, red patches appear.

Occasionally there are target lesions; they look like a bull's-eye like erythema multiforme.

Polymorphous light eruption

PMLE usually causes a burning sensation or itch that lasts several days.

PMLE may be a rare occurrence in the individual concerned or may occur every time the skin is exposed to sunlight. In most, it occurs each spring, provoked by several hours outside on a sunny day. If further sun exposure is avoided, the rash settles in a few days and is gone without a trace within a couple of weeks. It may or may not recur next time the sun shines on the skin. However, if the affected area is exposed to more sun before it has cleared up, the condition tends to get more severe and extensive.

In most individuals there is a hardening as the summer progresses and more sun can be tolerated without a rash appearing. However, this does not always occur, and some very sensitive individuals even develop PMLE in the winter.

PMLE is thought to be caused by an immune reaction to a compound in the skin which is altered by exposure to ultraviolet radiation. The result is an inflammatory rash. It is usually provoked not only by short wavelength UVB but also longer wavelength UVA. This means the rash can occur when the sunlight is coming through window glass, and that sunblocks may not be all that effective at preventing it.

Prevention

It is not known how to prevent PMLE altogether. However, many people can avoid developing a rash by using effective sun protection during the middle hours of the day from September to May (Southern Hemisphere summer). Others successfully manage to gradually harden their skin by slowly increasing how long they spend outdoors with uncovered skin.

• Cover all affected areas with clothing. The best fabrics have been tested for their protective qualities. Choose UPF 40+ clothing.
• Apply Broad Spectrum Sun Protection Factor 30+ semi-opaque sunscreen frequently to all uncovered skin.
• Stay in the shade.

Treatment

If your PMLE is severe, your dermatologist may recomend one of the following:

• Short course of oral steroids e.g. to cover a summer holiday.
• Polypodium leucotomas (Heliocare™)
• Beta carotene.
• Hydroxychloroquine.
• UVB or PUVA - a special form of ultraviolet treatment for several weeks in early spring.