ConditionSkin, hair & nails
Polymorphous Light Eruption (Sun Allergy)
Polymorphous light eruption (PMLE) is the most common sun-triggered rash, often called sun allergy or sun poisoning. Itchy red bumps, blisters or patches appear on sun-exposed skin, typically the chest, arms and backs of the hands, a few hours to a few days after the first strong sun of spring or a sunny vacation. The face is often spared. It clears in 1 to 2 weeks without scarring if you avoid more sun. Many people improve as summer goes on, a process called hardening. Sun protection and steroid creams usually control it.
Also called: PMLE, polymorphic light eruption, sun allergy, sun poisoning (informal), benign summer light eruption
At a glance
- What it is
- An itchy, delayed immune reaction to sunlight on skin that is not used to it.
- Who gets it
- About 1 in 10 to 1 in 5 people in temperate climates, more often women, often starting before age 30.
- Timing
- Hours to 3 days after sun exposure, mainly in spring and early summer.
- Look
- Red bumps, blisters or plaques on the chest, arms, hands and legs. Face often spared.
- Treatment
- Avoid further sun, steroid creams, antihistamines for itch, and preventive light therapy for severe cases.
When to get help
Call 911 or go to the ER
- Swelling of the face, lips or throat, or trouble breathing (not typical of PMLE, possible allergic reaction)
See a doctor within a day or two
- A widespread blistering rash with fever, chills, nausea or feeling very unwell after sun exposure (possible severe sunburn or a drug reaction)
- A rash with fever, joint pain, mouth ulcers or tiredness (possible lupus)
Book a routine appointment
- A sun rash that keeps coming back every year and affects your life
- A rash that does not clear within 2 weeks of avoiding sun, or leaves scars
- A rash that appears within minutes of sun exposure and fades within hours (possible solar urticaria)
- A sun rash after starting a new medicine
Usually safe to manage at home
- An itchy bumpy rash on the chest and arms a day after the first sunny day of the year, which you have had before
What causes PMLE
Sunlight, particularly UVA and also UVB, changes molecules in the skin. In most people, the immune system tolerates these changes because UV light slightly suppresses skin immunity. In people with PMLE, this suppression is reduced, so the immune system reacts against the sun-altered skin, causing inflammation.
With repeated, gradual exposure over the summer, the skin thickens and tans and the immune reaction often lessens. This is called hardening. PMLE often runs in families.
Symptoms
- itchy or burning rash on sun-exposed areas: V of the chest, outer arms, backs of the hands, legs and sometimes the face
- appears 30 minutes to several hours, sometimes up to 3 days, after exposure
- many forms ("polymorphous"), but each person tends to have the same type each time: - small red bumps (papules), the most common - clusters of tiny blisters - raised plaques - areas resembling insect bites or eczema
- clears within 7 to 14 days if more sun is avoided, without scarring
Sun through window glass can trigger it, because UVA passes through glass.
Who is at risk
- women more often than men
- people with fair skin, though it occurs in all skin types and is a recognized cause of rash in darker skin too
- onset usually in the teens to 30s
- people from cooler climates traveling to sunny destinations
- a family history of PMLE
Similar conditions
| Condition | How it differs |
|---|---|
| Sunburn | Painful redness within hours, followed by peeling, no bumps |
| Solar urticaria | Hives within minutes of sun exposure, fading within hours |
| Drug-induced photosensitivity | Exaggerated sunburn or rash after starting a medicine such as doxycycline, thiazides or NSAIDs |
| Cutaneous lupus | Rash develops more slowly and lasts weeks, may scar, may come with joint pain and positive ANA |
| Heat rash | Tiny bumps in sweaty, covered areas |
| Photoallergic dermatitis | Eczema-like rash where a sunscreen or fragrance was applied |
Diagnosis
PMLE is usually diagnosed from the typical history and appearance. A dermatologist may:
- take a skin biopsy if the diagnosis is unclear
- check ANA and Ro/La antibodies to rule out lupus
- perform phototesting or provocation testing with UV light in specialist centers
Treatment
During a flare
- Avoid further sun until the rash settles.
- Topical steroids (moderate to potent strength for a few days) reduce itching and inflammation.
- Oral antihistamines ease itch. Follow the label dose.
- Cool compresses and calamine lotion soothe the skin.
- Short course of oral steroids for severe flares, prescribed by a doctor.
Prevention
- Broad-spectrum, high-SPF sunscreen with strong UVA protection, applied generously 15 to 30 minutes before going out and reapplied every 2 hours. See sun protection.
- Protective clothing: long sleeves, tightly woven or UPF-rated fabrics, wide-brimmed hats.
- Gradual exposure: short periods of sun early in spring to build tolerance.
- Avoid peak sun from 10 a.m. to 4 p.m.
- Window film to block UVA in cars and homes if needed.
- Preventive phototherapy (desensitization): a course of controlled UVB or PUVA light therapy in early spring for people with severe, recurrent PMLE, which induces hardening.
- Hydroxychloroquine or other medicines for severe cases not controlled by other measures.
Outlook
PMLE is harmless and does not lead to skin cancer or lupus. It may recur every spring for years, but often becomes milder over time, and some people find it stops altogether.
Frequently asked questions
What does polymorphous light eruption look like?
It usually looks like clusters of small, itchy red bumps or tiny blisters on sun-exposed skin, such as the chest, arms and backs of the hands. It appears hours to a couple of days after sun exposure and fades within 1 to 2 weeks.
Is PMLE the same as sun poisoning?
"Sun poisoning" is an informal term used for both severe sunburn and PMLE. PMLE is an itchy immune rash appearing hours to days after sun exposure, while severe sunburn is a burn with pain, blisters and sometimes fever.
How do you get rid of a sun allergy rash fast?
Avoid further sun, apply a steroid cream to the rash, take an antihistamine for itching, and use cool compresses. The rash usually clears within 1 to 2 weeks. A doctor can prescribe stronger treatment for severe rashes.
Can sunscreen prevent PMLE?
Yes, partly. A broad-spectrum sunscreen with high UVA protection reduces flares, especially when combined with protective clothing and gradual sun exposure in spring. Some people still react and benefit from preventive light therapy.
Is polymorphous light eruption a sign of lupus?
No. PMLE is a separate, harmless condition. Lupus can also cause sun-triggered rashes, but these last longer and often come with other symptoms such as joint pain and fatigue. A doctor can test for lupus if needed.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Dermatology: Polymorphous light eruption; Sun allergy
- British Association of Dermatologists: Polymorphic light eruption patient information
- DermNet: Polymorphous light eruption
- MedlinePlus (US National Library of Medicine): Sun sensitivity
- Skin Cancer Foundation: Sun protection guidance