Many people mistake polymorphic light eruption (PLE) for heat rash, a common error that can lead to ineffective treatments, according to GP Dr. Philippa Kaye. Dr. Kaye, who also suffers from PLE, notes that while both conditions can cause red, blotchy skin, their causes and treatments are distinct.
Heat rash, often seen during hot weather, is essentially a "plumbing problem" where blocked sweat ducts trap sweat, causing irritation and small spots in areas where sweat collects, such as skin folds. The standard treatment involves keeping the skin cool and dry, wearing loose cotton clothing, and allowing it to settle.
PLE, however, is an abnormal immune reaction to ultraviolet (UV) light from the sun, not heat. It typically appears in spring or early summer when skin, unaccustomed to sun exposure after winter, is suddenly exposed to strong sunlight. The rash usually develops within hours or days of sun exposure.
A key differentiator is the location. PLE often affects skin not typically exposed to the sun, such as the chest or tops of feet, while areas that receive regular light exposure year-round, like the face and backs of hands, may be spared. The rash can manifest in various forms, including small red bumps, larger raised patches, or tiny blisters, and is typically intensely itchy. Unlike heat rash, PLE tends to affect women more commonly and often begins between the ages of 20 and 40, though the reasons for this are not fully understood.
While PLE is not dangerous and often resolves on its own within a week if sun exposure is avoided, the intense itching can be bothersome and impact quality of life, particularly during holidays or sunny spells. Treatment options for the itch include over-the-counter antihistamine tablets and emollients for dry skin. In more severe cases, steroid creams or a short course of oral steroids may be prescribed. For persistent or severe PLE, a referral to a dermatologist might be necessary. One treatment offered by specialists is desensitisation phototherapy, a controlled course of UV exposure to help the skin build tolerance.
Dr. Kaye emphasizes that prevention is key. While heat cannot be avoided during a heatwave, sun exposure can be managed by seeking shade, covering up with clothing, and using a high-factor, broad-spectrum sunscreen. She also cautions that if a rash does not improve within a week or two of avoiding the sun, is severe, spreading, blistering, or if there is uncertainty about its cause, medical advice should be sought. Skin conditions can resemble each other, and in rare instances, some may be signs of skin cancer, making proper medical assessment crucial.