When your skin suffers from UV stress

What is polymorphous light dermatosis?

Polymorphous light dermatosis (PLD) is the most common form of what people call a “sun allergy” and belongs to the group of photodermatoses – skin conditions triggered by sunlight. It usually appears a few hours to a few days after sun exposure. Areas exposed to the sun, such as the face, décolletage, upper arms, backs of the hands and thighs, are particularly affected.

The term “polymorphous” means “many‑shaped”, because the skin (epidermis) can react in different ways: from small blisters and pustules to large areas of skin changes, so‑called plaques. Typical features are itching, erythema and sometimes pain.

Polymorphous light dermatosis tends to occur especially when the skin is not yet accustomed to the sun – often in spring or at the start of a holiday. As the condition can be chronic, many people with photodermatosis experience the same symptoms each year after the first extended sun exposure.

Although polymorphous light dermatosis is the best known sun reaction, there are other light‑related skin responses such as solar urticaria or chronic actinic dermatitis. Overall, PLD is a classic sun‑related skin disorder that can significantly affect wellbeing.

Is a sun allergy a true allergy?

A “sun allergy” is not a classical allergy type like an allergy to pollen, house dust mites or food. In medical terminology the phrase “sun allergy” or “light allergy” does not really exist – it is used colloquially for various skin conditions triggered by sunlight.

Whether these reactions are genuine allergies is not yet conclusively established scientifically. For this reason diagnosis and treatment differ from classical allergies, such as those to pollen or animal hair. However, there is evidence that ultraviolet radiation can affect the immune system in a way that produces allergy‑like skin changes.

What causes polymorphous light dermatosis?

This unpleasant skin reaction can affect people of any age, but it usually begins within the first thirty years of life, so children can be susceptible. Women and people with fair skin types are particularly often affected, although other skin types can also be involved. Genetic factors are suspected to play a role, as the condition often runs in families.

When the sun's UV rays reach the epidermis, those affected may develop an overreaction of the immune system. UV exposure activates certain antigens in the skin tissue, attracting white blood cells and causing a local inflammation. Normally melanin, the pigment that tans the epidermis, protects against UV rays. In people with PLD this protection does not work as well – especially fair skin types produce less melanin and are therefore more sensitive.

The precise way a sun “allergy” develops is not fully understood. There are several theories: UV radiation might stimulate the production of free radicals in skin cells, which then overstimulate the immune system. Another hypothesis is that newly formed allergens produced by sunlight trigger the reaction. In any case, cells in people with photodermatosis are less able to neutralise these free radicals, resulting in an exaggerated immune response with red, inflamed areas.

In summary, polymorphous light dermatosis is a complex dermatological reaction to sunlight in which genetic predisposition, skin type and immunological processes interact.

Sun allergy – what symptoms do patients have?

Symptoms of polymorphous light dermatosis are usually delayed – often only a few hours to several days after sun contact. Areas that suddenly receive a lot of sun, for example the first sun exposure after winter or the start of a beach holiday, are particularly affected.

Typical findings are very itchy, patchy redness, mainly on the face, neck, décolletage, arms, backs of the hands and legs. The epidermis can show various changes: red spots, raised areas, small nodules or even pustules. Sometimes the rash can burn or become infected if scratched excessively.

The rash usually lasts a few days and resolves on its own if further sun exposure is avoided. Scarring normally does not occur, unless the skin surface is further damaged by scratching or infection. Many patients notice that symptoms ease over the course of the summer and disappear in autumn or winter.

Polymorphous light dermatosis occurs mainly in spring and early summer, when the epidermis is not yet used to the sun. For some people the rash appears each year, although complaints often become milder over time or disappear completely.

How can you distinguish sun allergy from sunburn?

Sunburn and sun allergy can sometimes look quite similar, but there are a few differences that help to tell them apart.

A sunburn usually appears within a few hours after sun exposure. The skin becomes diffusely red, feels hot and can be quite painful, especially when touched. This is mainly caused by UV‑B rays, which directly damage the epidermis. After about a day the skin typically begins to improve slowly.

A sun allergy, on the other hand, often takes longer to develop – sometimes symptoms only appear days later. It is mainly triggered by UV‑A rays and is thought to be due to a genetically determined hypersensitivity of the immune system, resembling an autoimmune reaction. The epidermis then reacts more with patchy redness, severe itching and small vesicles or pustules. Sometimes the skin surface may even develop darker spots for a longer time.

In short, sunburn is a rapid, painful reaction with diffuse redness, while sun allergy is a delayed, itchy and patchy skin change. 

When should you see a doctor for a sun allergy?

You should seek medical attention for a sun allergy if symptoms worsen or do not improve. It is particularly important to obtain immediate medical help if you experience additional circulatory problems such as dizziness, nausea or weakness – these can be signs of serious overheating or other complications.

Although sun allergy itself is usually more annoying than dangerous, a concurrent sunburn or heatstroke can worsen the situation. A severe sunburn can lead to overheating and even heat collapse, so a medical assessment is important to rule out all risks.

How does a doctor diagnose a sun allergy?

To diagnose a sun allergy, the doctor usually starts with a detailed history, asking when and where symptoms occur, whether similar rashes have occurred before and which medications are taken. This history often provides important clues.

To confirm the diagnosis a light test (photoprovocation test) is often performed: specific skin areas, usually on the inner upper arm, are irradiated for several days with controlled doses of UV light (UV‑A and UV‑B). If typical reactions such as redness or irritation appear at these sites after a few hours, this is a fairly clear sign of a sun allergy.

If a reaction triggered by chemical substances is suspected, a photo‑patch test can be carried out. Suspected triggers (for example components of cosmetics) are applied to the skin and the area is then exposed to UV light. If only the irradiated site shows a skin reaction, the trigger has probably been identified.

In some cases the doctor takes a small skin sample (biopsy) for microscopic examination to rule out other conditions. Additional blood tests may be useful if an underlying disease such as lupus is suspected.

Managing sun allergy: best tips against polymorphous light dermatosis

• Antihistamines can help reduce the distressing itch that often accompanies photodermatosis. They are available as tablets or creams, but should be used in consultation with a doctor.
• For severe inflammation or pronounced symptoms the doctor often prescribes corticosteroid medications. These are anti‑inflammatory and help relieve symptoms quickly.
• Well‑cared‑for skin is more resilient. Moisturising creams containing ingredients such as hyaluronic acid or glycerin help strengthen the skin barrier and prevent dryness.
• As soon as you notice initial symptoms such as itching or redness, you should move out of the sun immediately. Continued sun exposure can worsen the skin reaction and delay healing.
• Cool compresses or cold packs help calm the epidermis and relieve itching. Important: never place the cold pack directly on the skin surface; wrap it in a cloth to avoid frost damage.
• Aloe vera has anti‑inflammatory and moisturising properties. A gel from the plant or a related product can soothe the epidermis and support the healing process.
• Cottage cheese (quark) has a cooling and anti‑inflammatory effect. Simply put cold quark on a cloth and apply to the affected skin areas – this gently relieves itching and redness.
• After‑sun products containing photolyase can accelerate skin regeneration. This active ingredient is an enzyme derived from algae that helps the skin repair UV‑induced damage. 
• Natural remedies such as green or chamomile tea, coconut oil, oatmeal baths, cucumber compresses or calendula ointment can soothe the skin and ease itching – ideal as gentle complements to medical treatment.
• As hard as it may be, avoid scratching itchy areas. Scratching can further injure the epidermis, promote inflammation and even cause infections.
• After winter, the skin should be gradually accustomed to the sun. Short periods outdoors and a gradual increase in sun exposure help make the epidermis more resilient.
• A dermatologist can perform controlled UV‑B irradiation to gradually accustom the skin to UV radiation. This so‑called hardening therapy can reduce the frequency and severity of symptoms.
• Always use sunscreens with an SPF of at least 30 and ensure they provide both UV‑A and UV‑B protection. This effectively protects the epidermis from harmful solar radiation.
• Apply sunscreen about 20–30 minutes before sun exposure and reapply every two hours or after swimming and sweating to maintain protection.
• Long‑sleeved shirts, long trousers and wide‑brimmed hats provide additional protection from the sun. Special UV‑protective clothing offers a tested protection factor and is particularly recommended for those with strong sun sensitivity.
• The sun's rays are strongest between 11:00 and 15:00. If possible, seek shade or stay indoors during this time to avoid unnecessary strain on the epidermis.
• Perfumes, deodorants or make‑up can increase photosensitivity and intensify the reaction. It is therefore advisable to avoid such products before sun exposure.
• UV‑A rays penetrate window glass, for example in cars or offices. If you are sensitive, it may be sensible to use protective measures such as special films or protective clothing in these situations too.
• On holiday, prefer sunscreens from Europe if possible, as they meet particularly strict quality standards and provide reliable protection. Always take enough sunscreen and any required medications with you when travelling to stay protected on the go.
• Some medications (including antibiotics, heart medicines, antidiabetics and rheumatism treatments) can increase skin photosensitivity. Talk to your doctor or pharmacist to find out whether your medicines may raise the risk of a sun allergy.
• A balanced diet with omega‑3 fatty acids (for example from salmon), vitamin C, vitamin E and quercetin (in fruits and vegetables) can support skin health and strengthen the skin's defences.

Polymorphous light dermatosis is often an underestimated skin condition that can affect the lives of many sun lovers. But if recognised early and managed appropriately, you do not have to miss out on the pleasures of summer. With the right knowledge and strategy, you can enjoy the sun again without worry – and without troublesome skin problems.