Sun Allergy (Polymorphic Light Eruption): Causes and Relief

An itchy rash that appears a few hours to a couple of days after time in the sun, usually on the arms, the V of the neck, the chest or the legs, is most often polymorphic light eruption (PMLE), the most common type of sun allergy. It usually settles on its own within about a week if you stay out of strong sun, and flares can often be prevented with gradual sun exposure, protective clothing and a broad spectrum sunscreen.

Many people in India notice this rash at the start of summer, after a trip to the hills or the beach, or after a long outdoor event. This guide explains why it happens, what it looks like on brown skin and when you should see a dermatologist.

What is polymorphic light eruption?

Polymorphic light eruption, also called polymorphous light eruption, is a rash caused by an abnormal reaction of the skin to sunlight. The British Association of Dermatologists (BAD) describes it as the most common rash caused by ultraviolet (UV) light. The word polymorphic means many forms, because the rash can look different from one person to another.

Key facts from the NHS, DermNet and the BAD:

• Timing: the rash appears within a few hours to a few days of sun exposure
• Season: it is more common in spring and early summer, when skin meets strong sun after months of less exposure
• Trigger: mostly UVA light, sometimes UVB or visible light. As little as 20 minutes of sun can trigger it in some people
• Through glass: because UVA passes through window glass, it can appear after sitting by a sunny window
• Who gets it: it is more common in women and people under 40, and about 15% of people with PMLE have a family member with it
• Hardening: as the season continues, the skin often gets used to sunlight and flares become less likely

PMLE is reported more often in fair skin and in less sunny countries, but it affects all skin types and is seen in Indian skin as well.

What does a sun allergy rash look like?

The NHS describes the rash as:

• Small raised spots or blisters, or larger blotchy areas
• Itchy or burning
• Red or pink, which may be harder to see on brown skin

On brown and black skin, the BAD notes that a pinpoint rash of tiny bumps is commonly seen. The rash usually appears on areas that are normally covered and then suddenly exposed, such as the forearms, the back of the hands, the V of the neck, the upper chest and the legs. The face is often less affected because it is exposed year round.

Why does it happen in India?

Strong sunshine for much of the year makes Indian summers, hill station holidays and beach trips common triggers. Situations that often come before a flare include:

• The first hot weeks of March to May
• A holiday to the mountains, where UV can be stronger at altitude, or to the coast
• Weddings, outdoor functions, pilgrimages or sports days in the sun
• Wearing sleeveless or short sleeved clothes after usually covering the arms
• Long car, bus or train journeys by a sunny window

Could it be something else?

Several conditions can look like a sun allergy:

Condition	Clues
Prickly heat (miliaria)	Tiny bumps in sweaty, covered areas, often in humid weather, not linked to sunlight itself
Sunburn	Painful redness within hours, in all exposed skin, after too much sun
Phytophotodermatitis	Streaks or splash marks where lime, lemon or certain plant juices touched the skin before sun exposure
Drug or product photosensitivity	Rash on sun exposed skin after starting a new medicine or applying certain products
Hives (urticaria)	Raised wheals that come and go within hours
Lupus and other conditions	Rash with joint pain, tiredness or other symptoms

DermNet’s photosensitivity page explains that some medicines and chemicals make the skin more sensitive to sunlight. Never stop a prescribed medicine on your own, but tell your doctor if a rash on sun exposed skin started after a new medicine.

Read more about prickly heat and monsoon skin care and hives if your rash looks more like those.

What can I do at home when the rash appears?

The NHS suggests:

1. Stay out of the sun until the rash settles. Continued exposure makes it last longer or spread
2. Cool the skin with calamine lotion or a plain moisturiser
3. Ask a pharmacist or doctor about an antihistamine if the rash is very itchy
4. Wear loose, covering cotton clothes over the rash
5. Do not scratch, as this can leave dark marks on brown skin

Avoid applying steroid creams bought without a prescription, home remedies such as lemon juice, or strong perfumed products on the rash.

How can I prevent sun allergy flares?

Prevention works better than treatment. Advice from the NHS and the BAD includes:

• Avoid the strongest sun. The NHS advises staying out of the sun between 11am and 3pm. In India, the late morning and early afternoon sun is very strong for most of the year
• Use a broad spectrum sunscreen that protects against UVA and UVB. The NHS recommends a high SPF of 50 or more, applied 15 to 30 minutes before going out and reapplied every 2 hours. Our sunscreen guide for India explains SPF and PA ratings
• Cover up with long sleeves, a wide brimmed hat, a dupatta or scarf over the neck, and an umbrella
• Expose your skin gradually at the start of summer. The BAD notes that gradual exposure in spring may reduce the severity of the rash in people with mild PMLE
• Use window film or curtains on long journeys if glass triggers your rash

How does a dermatologist treat polymorphic light eruption?

Most cases are mild and settle with sun protection. If the rash is severe, frequent or affecting your daily life, your dermatologist may:

• Confirm the diagnosis and rule out conditions such as lupus, drug photosensitivity or contact allergy, sometimes with blood tests or a skin biopsy
• Prescribe an anti inflammatory cream for a short period during flares
• Suggest antihistamines for itch
• Recommend desensitisation phototherapy, in which the skin is given gradually increasing doses of UV light under supervision before the sunny season, as described by the BAD
• Review your medicines and skin products for anything that increases sun sensitivity

Dark marks after the rash settles are common in Indian skin and usually fade gradually with strict sun protection.

When to see a dermatologist

See a dermatologist or doctor if:

• The rash is getting worse or has not improved after one week, as the NHS advises
• The rash is very swollen, blistered or widespread
• You also have joint or muscle pain, extreme tiredness or a fever
• The rash appears on the face every time you step outside
• It started after a new medicine or skin product
• Sun allergy is stopping you from working, travelling or attending events
• You keep getting dark patches after each flare

If you are not sure whether your rash is a sun allergy, prickly heat or something else, Dr. Maria offers online consultations where you can share photos taken during a flare and discuss prevention for the summer ahead.