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1 in 10 people have a sun allergy – and the figure is rising

4/7/2023

Translation: Katherine Martin

While many people love being sun-kissed, there are a few who prefer to steer clear of the sun’s rays. The reason? Their light-sensitive skin reacts to UV radiation by coming out in an itchy rash. Though said to be caused by an allergy, this technically isn’t the case for 90 per cent of those affected.

Imagine you’re a fashion model, scheduled to do a photoshoot somewhere tropical. However, instead of photos of tanned skin against a beach backdrop, all you get are images of itchy pustules, burning weals, red spots, swelling and blisters. This is exactly what happened to David Koch, one of Germany’s most internationally successful models, and sufferer of the condition known as polymorphic light eruption (PMLE). Accounting for about 90 per cent of all photo- or light-induced dermatoses, PMLE is one of the most common skin conditions triggered by sunlight.

An overreaction, not an allergy

Symptoms like the ones David Koch experiences are colloquially referred to as sun allergies. «PMLE isn’t an allergy in the traditional sense of the word, i.e. in the sense that the body reacts to foreign bodies by producing antibodies,» says Dr. Ichiro Okamoto MD, attending physician in the Department of General Dermatology at the Medical University of Vienna. Skin can’t have an allergic reaction to sunlight. At least, no allergen forming in the body as a result of sun exposure has ever been identified. What the skin can do is react to the UV contained in sunlight in a hypersensitive manner. This is especially true of UV-A radiation (wavelengths of 340–400 nm).

Sun exposure usually results in skin changes – the skin tans and thickens, and the body’s defences are able to tolerate it. The reason why this isn’t the case for PMLE sufferers, and why their immune systems overreact, hasn’t yet been studied sufficiently. «It’s possible that oxidative stress is a factor. This is because UV-A radiation causes aggressive free radicals – which play a significant role in inflammation – to form in the skin,» Okamoto says. «Unlike in healthy people, it’s believed that the defence mechanisms present in the cells of people with PMLE are impaired, meaning the skin can’t fight off these free radicals.»

Putting a damper on beach holiday fun

For most people with PMLE, the condition isn’t the career risk it was for David Koch. As the word «polymorphic» in the name suggests, the symptoms can be very different from person to person and can also vary in severity.

«A lot of people are able to cope with it – only five per cent consult a doctor,» says Trier-based dermatologist Dr. Dierk Steinmann (site in German). For many people, though, the joy of a beach holiday or an al fresco lunch, is, at the very least, dampened. «These unsightly and, more importantly, itchy patches of skin can severely impair the quality of life of those affected,» Okamoto says.

At least 10 per cent of people are affected

According to Immunologiezentrum Zürich (The Zurich Centre for Immunology), 10 to 20 per cent of the population at this latitude has PMLE – and the numbers are increasing. Women are affected in nine out of ten cases, with the condition mostly presenting within the first three decades of life. It also occurs when the skin is exposed to intense sunlight again after a long sunshine-free period.

«That’s also why PMLE cases peak in spring and early summer,» Steinmann says. In the cooler months, the disease often hits travellers heading to sun-soaked parts of the southern hemisphere. Those affected develop itchy, blotchy or blister-like red skin rashes on the areas of their bodies exposed to sunlight. The symptoms can set in between a few hours and several days after a long sunbathing session. While PMLE often shows up on the neck, hands, arms, chest and legs in adults, in children, it often afflicts the face.

Choosing the right SPF

The good news is that unlike sunburn, PMLE doesn’t cause permanent skin damage. In many cases, repeated sun exposure also leads to habituation, with symptoms becoming less severe over time. That being said, this effect unfortunately only lasts for one sunny season, with the symptoms usually striking again the following year.

To prevent or at least curb them, PMLE has to be diagnosed. Getting a diagnosis means your dermatologist will be able to give you appropriate sun-protection advice if you can’t – or don’t want to – avoid the sun. «When it comes to typical sun protection i.e. for preventing sunburn, UV-B filters do the job.However, PMLE sufferers should use physical sunscreens that also contain highly effective UV-A filters with at least factor 30,» advises Steinmann.

Products that contain, for example, alpha-glucosylrutin, come highly recommended. «To prevent, for example, Mallorca acne (see below), you should go for unscented products. For adults, gels are best. Sunscreen also needs to be applied in a timely manner. It takes at least 30 minutes to be effective. And, of course, if you’re swimming or snorkelling, you’ll need a waterproof one.»

Get set for the sun

It’s also important to slowly increase your sun exposure. For instance, during the first few days of a beach holiday, this might involve taking siestas (after midday) in the shade and wearing light clothing and a wide-brimmed hat when the sun’s at its strongest. «For some, very severe cases, light therapy can also prove useful,» says Steinmann. «This involves, say, four weeks before a beach holiday, preparing for intense sun exposure. It works by way of exposing the body to increasing doses of UV-A or UV-B light, depending on which radiation component triggers the skin condition – something that can be determined through testing. To avoid overdose, the therapy should be carried out by a dermatologist.»

You can also build up at least a little sun protection on the inside by regularly taking beta-carotene capsules, starting about 4–5 weeks before your holiday. «The plant pigment is deposited in the skin, allowing parts of the UV radiation to be intercepted by the upper layers of the skin. It also staves off free radicals in the skin, which develop every time you sunbathe.»

If, despite all these precautions, you still come out in a rash, you can ask your doctor to prescribe an anti-itching, anti-inflammatory ointment or antihistamines. Cooling compresses and mild corticosteroids can also relieve acute symptoms.

Deal with symptoms quickly

If it’s the first time you’ve ever got a rash after sunbathing, Dr. Okamoto gives the following advice: «Immediately start avoiding contact with the sun and see a dermatologist right away. This will allow the acute-stage skin changes that characterise the condition to be recognised and a correct diagnosis to be reached.» If your symptoms have already either slightly or totally subsided, finding the cause and differentiating it from more serious, light-related reactions, such as a photoallergic reaction or solar urticaria (hives) becomes more difficult.

To rule these out, the dermatologist will carry out a diagnostic interview, inquiring about factors such as pre-existing medical conditions, medications you’re taking, the sunscreen you use and the symptoms you’re experiencing.

Mallorca acne: a special form of PMLE

Another, relatively harmless, variant of PMLE is Mallorca acne (acne aestivalis). The name says it all: «A few days after sunbathing, itchy nodules resembling acne pustules appear,» Okamoto says. The culprits are the emulsifiers in greasy sunscreens. When they interact with UV-A light, they form substances that inflame the hair follicles. The chest, arms, shoulders, neck and back are most severely affected. Those most likely to be at risk are women aged 20 to 40.

These skin changes subside on their own without scarring, but until then, cool packs or cooling gels can relieve the symptoms. Undergoing mild acne therapy or using a cortisone cream might also be an option if necessary. In severe cases, antihistamines may prove useful.«To prevent the condition, it’s best to avoid using oily sunscreens. Grease- and emulsifier-free sunscreens in gel form are ideal.»

Could it be a photoallergy? Identifying the allergen

As well as PMLE, there are other, far rarer forms of light-related skin diseases. When referring to these conditions, the term «sun allergy» is much more appropriate – a prime example of these being photoallergic reactions. As is the case with PMLE, however, the sun itself doesn’t trigger the allergy. Instead, this is done by a substance that makes its way into the skin, either from inside or outside it, before changing its structure as a result of sun exposure.

Examples of these substances might be ingredients found in body lotions or drugs such as antibiotics and antidepressants. The UV irradiation turns the initially harmless substance into an allergen, which the immune system then fights.

«A photoallergic reaction occurs one to three days after sun exposure, presenting as blisters and itching, possible oedema, redness, flaky skin and pimples,» Okamoto explains. Photo patch testing, during which potential allergens are applied to the back and then irradiated with UV light, allows the substance in question to be identified and, subsequently, avoided. «However, since stopping taking medication isn’t always possible – or might even be dangerous – adequate sun protection is especially important in these cases.»

Phototoxic reactions

Phototoxic reactions are far more common. These arise without any involvement from the immune system. Chemical or natural compounds found in perfumes, medicines, cosmetics or body lotions react with the skin cells under the influence of UV-A rays. This forms free radicals that cause skin damage.

«Plant juices or the essential oils of citrus fruit, St. John’s wort and bergamot in particular can trigger this reaction. It resembles a very severe sunburn, and oedema and blisters often form as well,» Okamoto says. The severity of the phototoxic reaction depends on the strength and duration of sun exposure as well as the dose of the triggering substance. Even when sunlight is avoided, the symptoms are slow to subside.

«As well as avoiding sun exposure, cortisone ointments and cooling compresses can soothe the areas of the skin exhibiting changes.» To prevent this, you should avoid perfumed and phototoxic products (read the package insert). «It’s also best to use a fragrance-free sunscreen.»

Light urticaria: rare but dangerous

While the skin reactions mentioned above take time to appear, light urticaria (solar urticaria, commonly known as hives) shows up very quickly: «Within minutes of sun exposure, welts and skin redness occur, often accompanied by severe itchiness. Histamine is released in the cells, triggering the typical symptoms,» Okamoto says.

The welts usually die down after a few hours if the sun is avoided. In the meantime, cooling the affected area provides relief. However, in rare cases, when large areas of skin are affected by hives, the patient’s blood pressure may also drop, causing them to collapse.

A blessing or a curse?

«Sun allergies» aren’t usually dangerous. In fact, some experts see them as advantageous; people who suffer from them avoid long sunbathing sessions and ensure they’re well protected against the sun. As a result, they reduce their risk of developing skin cancer.

Header image: Joseph Barriento via unsplash

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Daniela Schuster

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oliver.fischer@digitecgalaxus.ch

If my job didn't exist, I'd definitely invent it. Writing allows you to lead several lives in parallel. On one day, I'm in the lab with a scientist; on another, I'm going on a South Pole expedition with a researcher. Every day I discover more of the world, learn new things and meet exciting people. But don't be jealous: the same applies to reading!

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