Polymorphous light eruption
Polymorphous light eruption (PMLE) is the most common immunologically mediated photodermatosis, presenting as a pruritic eruption of papules, papulovesicles, or plaques on sun-exposed skin that begins hours to days after ultraviolet exposure and characteristically improves as summer progresses ('hardening'). Mild eruptions are treated with a potent topical corticosteroid applied once or twice daily for 5 to 7 days, and severe eruptions with a short course of oral prednisone 30 mg once daily for 4 to 5 days, alongside sun protection with a broad-spectrum SPF 30+ sunscreen as the mainstay of prevention.
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What this article covers
- Overview
Definition: polymorphic light eruption (PMLE), sometimes called "sun poisoning" or "sun allergy," is the most common immunologically mediated photodermatosis: a pruritic rash on sun-exposed skin…
- Epidemiology
Prevalence increases with latitude in most regions: reported prevalence ranges from roughly 1 percent in China to over 20 percent in some northern European countries, though this gradient is not seen within Europe itself.
- Risk factors
Female sex, particularly in the first three decades of life.
- Pathophysiology
Lack of normal UV-induced immunosuppression: UV exposure normally suppresses cutaneous T cell immune responses, but this protective immunosuppression appears deficient in PMLE, permitting an…
- Clinical features
Hallmark presentation: a pruritic eruption of papules, papulovesicles, or plaques on sun-exposed skin, resolving within days without scarring if further sun is avoided, and recurring in the same…
- Differential diagnosis
Actinic prurigo: occurs mainly in children and, unlike PMLE, tends to persist through summer and can extend into winter; cheilitis and/or conjunctivitis are almost always present in actinic prurigo but not in PMLE.
- Diagnosis
The diagnosis is primarily clinical: a pruritic papular or plaque eruption on sun-exposed skin, plus a history of a similar eruption in spring or early summer that gradually improves as summer…
- Management
First, for mild eruptions, treat with a potent (group 1 to 3) topical corticosteroid such as clobetasol propionate 0.05% (0.5 mg per g), applied once or twice daily to affected areas for 5 to 7 days…
- Complications
Impact on quality of life: patients with PMLE spend less time outdoors and take fewer vacations than the general population, despite the condition being medically benign.
- Prognosis
Recurrent but self-limited each season: individual eruptions resolve within days if sun exposure is avoided, and the overall disease is recurrent, often persisting for years.
- Prevention
Broad-spectrum sunscreen (UVA and UVB), sun protection factor (SPF) 30 or higher, applied regularly and generously, is first-line; SPF 45 sunscreen at 2 mg/cm2 prevented PMLE in all 15 subjects in one repeated-exposure study.
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