Polymorphic Light Eruption
Also known as
Polymorphous light eruption
What is polymorphic light eruption?
Polymorphic light eruption is a sunlight-sensitive rash (photodermatosis) on skin that has been exposed to sunlight. As the name “polymorphic” suggests, the rash can present in many different forms from tiny red pin-head sized spots through to large patches of redness.
What causes polymorphic light eruption?
Polymorphic light eruption results from exposure to sunlight in those who are predisposed to developing the condition. In Australia, it is more frequently seen in the southern states. Polymorphic light eruption affects more females than males and is more common in fair skinned individuals between the ages of 20 to 40 years.
Polymorphic light eruption is usually seasonal. It appears in early spring after the skin has been protected from sunlight over the winter months. The rash appears either rapidly within hours or within days after sun exposure. The amount of sunlight required to trigger the condition is highly variable, ranging from minutes to hours. Both UVB and UVA wavelengths can trigger the rash.
What does polymorphic light eruption look like?
The rash usually appears on sun-exposed areas of the skin such as the chest, neck, arms and face. The rash can vary in appearance – it may look like multiple raised red spots and dots, or itchy pin-sized lumps, or it can look like hives. The rash may be itchy or cause a burning or stinging sensation. The rash usually fades within 2 to 7 days without leaving a mark.
Over time, most sufferers experience a phenomenon known as “skin hardening” which means that the skin develops a tolerance to sunlight after repeated sun exposure. The condition usually improves over the summer months or with further UV exposure (e.g. phototherapy).
How is polymorphic light eruption diagnosed?
The diagnosis is usually made by a dermatologist based on the history of events leading up to the rash and the characteristic appearance of the rash.
In some cases a blood test, urine sample or stool sample may be needed to exclude other photodermatoses such as lupus erythematosus or erythropoietic protoporphyria.
A skin biopsy may be needed to confirm the diagnosis. Phototesting may be undertaken in a specialist clinic to confirm the diagnosis.
How is polymorphic light eruption treated?
Polymorphic light eruption is prevented by appropriate sun protection which includes avoiding the sun, wearing protective clothing and sunglasses, as well as the appropriate use of sunscreens. Supplements such as beta carotene and nicotinamide (vitamin B3) may be helpful in preventing polymorphic light eruption.
Medically supervised phototherapy may be prescribed to “harden” the skin if the condition persists or continues to be particularly troublesome. Exposure to natural sunlight in a graduated manner can also “harden” skin, however, this method is not recommended as the risk of developing skin cancer is increased. Sun beds or tanning booths are not medically prescribed equipment and are not safe.
Other treatment options include medications such as topical steroid creams, oral prednisolone or prednisone, hydroxychloroquine, azathioprine and thalidomide.
What is the outcome for polymorphic light eruption?
Most people with polymorphic light eruption will experience seasonal flare-ups of the condition especially at the beginning of sunnier weather. In Australia, most cases occur at the beginning of spring (September and October). Preventative treatments such as “skin hardening” may be considered several weeks prior to this time of year.
For people known to be at risk of developing polymorphic light eruption, medication may be prescribed as a form of prevention, particularly when planning a trip to a sunny location.
This information has been written by Dr Davin S. Lim