Polymorphic light eruption (sun allergy)
Polymorphic light eruption is the most common skin reaction to sunlight. The rash appears a few hours to a day after sun exposure, typically in early spring…
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Medicines commonly prescribed for Polymorphic light eruption (sun allergy)
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 10 mg cetirizine dihydrochlorideActive substance: cetirizineManufacturer: Ucb Pharma S.A.Prescription requiredDosage form: Cream, 0.1 gActive substance: mometasoneManufacturer: Almirall Hermal GmbhPrescription requiredDosage form: TOPICAL SOLUTION, 1 mg/gActive substance: mometasoneManufacturer: Organon Salud S.L.Prescription required
Polymorphic light eruption is the most common skin reaction to sunlight. The rash appears a few hours to a day after sun exposure, typically in early spring or during the first days of a holiday, and clears on its own within a few days. It is not an allergy in the usual sense and not a burn: the skin is reacting to ultraviolet light it has lost tolerance for over the winter. Its most useful practical feature is that the skin gradually adapts, and by midsummer the rash often stops appearing.
How it looks
- the rash appears 2–24 hours after sun exposure, sometimes up to three days later;
- small itchy red papules, blisters, raised patches or a mixture — hence the name "polymorphic";
- in any given person the rash looks the same each time;
- marked itching or burning;
- located on areas that were covered in winter and are now exposed: upper chest, shoulders, outer arms, neck, lower legs;
- the face and hands are less often affected — they get sun all year round;
- it clears in 2–7 days without scarring, provided you stay out of the sun;
- more common in women and usually starts at a young age.
An important detail: the reaction can be triggered by light coming through glass or thin clothing, which is why people sometimes fail to connect the rash with the sun.
What it is not
Similar rashes occur in other conditions, and it is worth telling them apart because the approach differs:
- sunburn — appears sooner, is uniform redness without papules, and hurts rather than itches;
- drug phototoxic reaction — looks like an excessive burn from ordinary sun; some antibiotics, diuretics, anti-inflammatories and acne medicines are implicated;
- solar urticaria — appears within minutes and clears within hours;
- lupus and other autoimmune conditions — the rash is persistent and comes with other symptoms;
- reactions to cosmetics and fragrances combined with sunlight;
- rare inherited disorders in which the skin reacts to light very severely.
When to see a doctor
- the rash returns every year and spoils your spring and your holidays;
- the reaction is triggered by very little sun;
- it does not clear within a week in the shade;
- blisters, marked swelling or fever develop;
- you take medication and your reaction to sun has become much stronger — reason to review the drug;
- the rash comes with joint pain, weakness, hair loss or a butterfly rash on the face;
- the reaction has appeared for the first time in adulthood;
- the rash leaves persistent marks or scarring.
How it is diagnosed
The description is usually enough: the link with sun, the delay of several hours, the location on exposed areas and the recurring pattern. Photographs are helpful. If the picture is atypical, autoimmune blood tests, a skin biopsy and sometimes photoprovocation testing at a specialist centre are arranged. The doctor will always review your medicines and cosmetics.
Prevention
This is the main part: prevention is far easier than treatment.
- build up the skin's tolerance gradually — in spring, start with 10–15 minutes of sun and increase slowly. This is exactly the mechanism by which the rash disappears by summer;
- broad-spectrum sunscreen with a high factor and strong UVA protection — UVA is the main culprit here. Apply generously and reapply every two hours;
- tightly woven clothing and a wide-brimmed hat; thin fabrics let ultraviolet through;
- avoid the sun during the middle of the day, roughly 11 am to 4 pm depending on region and season;
- remember that water, sand and snow reflect light, and that clouds barely block it;
- check with your doctor whether any of your medicines are photosensitising;
- for severe cases, your doctor may prescribe a course of phototherapy in spring — controlled "hardening" of the skin before the season.
Treatment
- get into the shade and stop further exposure — nothing else works without this;
- cool compresses and cool showers;
- emollients and soothing lotions;
- topical corticosteroids in a short course for itch and inflammation;
- antihistamines;
- oral corticosteroids in a short course only for a severe reaction;
- preventive phototherapy before the season, prescribed by a dermatologist;
- for very severe forms, immunosuppressants or hydroxychloroquine.
Common questions
Will it go with age? In many people the reaction weakens over the years and in some it disappears entirely.
Can I sunbathe? Moderately and gradually, yes. It is sudden intense exposure that triggers the rash.
Why does it stop by late summer? The skin has adapted to the ultraviolet. Next spring it starts again.
Will a sunbed help? Using one on your own initiative as "preparation" is not advisable — it is uncontrolled exposure with risks of its own. If the skin needs hardening, it is done under dermatological supervision.
Do I need sunscreen in the city? In season, yes, on the areas that react.
Online consultation
In an online consultation the doctor reviews photographs and the timing of the rash, helps distinguish it from a drug reaction and from autoimmune conditions, reviews your medicines and cosmetics, and works out a plan for the sunny season with you.
This material is for information only and does not replace a medical consultation.
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Reviewed on Aug 8, 2026
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