Polymorphous light eruption ("sun allergy"): causes, symptoms and prevention
If an itchy rash appears on your arms or chest a few hours after the first strong sun of spring, or on day two of a beach vacation, it may be polymorphous light eruption (PMLE), the condition many people call "sun allergy" or "sun poisoning."
- PMLE is a delayed immune reaction to UV light, mostly UVA, that shows up hours to a day or two after sun exposure.
- It's most common in women aged 20 to 40 and in people with fair skin, and it tends to fade as summer goes on.
- Prevention is broad-spectrum SPF 50+ sunscreen, protective clothing and shade; a doctor can add treatments for frequent flares.
What it is
According to DermNet: Polymorphic light eruption, PMLE is a seasonal sensitivity to sunlight that occurs in spring and early summer. It's a delayed hypersensitivity reaction: UV light triggers an inflammatory response to an as-yet-unknown antigen in the skin. DermNet says it's primarily caused by UVA (in 75 to 90% of cases) or by UVB, alone or together, and rarely by visible light. Because UVA passes through window glass, flares can happen even indoors or in a car.
Who gets it
- Most often people aged 20 to 40, and about four times more common in women than men.
- All skin types, but more prevalent in Fitzpatrick skin type I (see Fitzpatrick skin types).
- More common in places where sun exposure is uncommon: DermNet notes it may affect 20 to 40% of northern European women vacationing in the Mediterranean.
- A family history is reported in 15 to 46% of cases.
Symptoms and timing
The rash typically appears within several hours to one or two days of sun exposure and can last days to weeks, clearing faster if you stay out of the sun. As the name ("many forms") suggests, it can look like small bumps, blisters or raised patches. Over the summer, many people develop "hardening," where repeated exposure makes flares less likely. That's why the face and hands, which get sun all year, are often spared. In darker skin, the most common form is clusters of pinhead-sized bumps.
It resolves without scarring, and DermNet reports 60% of people see improvement or resolution over 15 years.
Prevention
- Broad-spectrum SPF 50+ sunscreen with good UVA protection (see SPF and broad spectrum explained).
- Sun-protective clothing (see UPF clothing).
- Shade, and sitting away from windows.
- Increasing sun exposure gradually in spring.
Medical treatment
For frequent or severe flares, DermNet lists options a doctor may consider, including topical or short courses of oral corticosteroids, carefully supervised phototherapy in early spring to induce hardening, hydroxychloroquine, and nicotinamide taken in the weeks before the usual flare season. It also lists afamelanotide, a prescription implant approved for a different light-sensitivity disorder (see afamelanotide (Scenesse)). That is a regulated medicine prescribed by specialists and is not the same as unregulated "melanotan" products (see melanotan risks).
When to see a doctor
Other conditions can look like PMLE, including lupus, solar urticaria, porphyria and drug-induced photosensitivity (see medications that cause sun sensitivity). DermNet notes diagnosis relies on excluding these, sometimes with a biopsy or blood tests, so get a new sun-triggered rash checked.
Educational information only, not medical advice. See a board-certified dermatologist for diagnosis and treatment. See our medical disclaimer.
Published October 28, 2026. Sources are linked in the text. See our Medical Disclaimer.