What is polymorphous light eruption (sun allergy)?

 

The summer sun entices us to venture outdoors and inevitably spend more time lapping up the warmth of the sun. In this time, sunbathing replenishes our vitamin D levels, boosts our mood and strengthens our immune system. But it most likely comes as no surprise to you that the sun’s UV rays can also have unpleasant consequences for the skin, which are sometimes not easy to diagnose or understand.^[1]

The skin is our largest organ, accounting for 16 per cent of our body weight. We have three layers of skin to protect us from the environment, which are directly exposed to it. So, it’s really no wonder that we need to look after our skin and know what might trigger certain skin reactions. 

In this article, we shed some light on skin conditions that are linked to sun exposure – such as a sun allergy – who is most often affected, sun allergy symptoms and how to prevent and treat them. Furthermore, find out what you can do to protect irritated skin from UV radiation – but crucially, how the sun’s UV rays are also important for our overall health.

What is a sun allergy?

Sun allergy, also called polymorphous light eruption, is a condition where the skin changes after sun exposure. Parts of the body that are affected by the rashes caused by a sun allergy are mostly, but not always, those that are exposed to the sun.^[3] Around 10 to 15 per cent of the UK population is believed to be affected by polymorphic light eruption.

Common areas affected are the chest, the skin below and above the elbow and the back of the hand. The face is not always affected by sun rash. Skin reactions can vary from person to person; however, people affected by sun allergy will find that their personal symptoms will not change greatly.^[2] In addition, sun allergy symptoms usually appear in early summer, at the beginning of the sunny season, and subside over the course of the summer.^[3]

Did you know that the term ‘sun allergy’ is colloquial? A sun allergy is not an allergy to sunlight itself, but a reaction to an allergen formed by UV radiation.^[4] The correct scientific term used is ‘polymorphous light eruption’.^[4]

Sun allergy symptoms: what does a sun allergy look like? 

Sun allergy symptoms often include itching or burning skin lesions – a sun allergy rash – after exposure to the sun. Changes to your skin can occur in many forms and can differ from person to person. Where some people may find that sun allergy symptoms rarely emerge, others are affected every time their skin is exposed to the sun.^[13]

The symptoms of a sun allergy usually appear within hours after sun exposure – in rare cases, even after two to three days.^[1] If you acclimatise to sun exposure slowly, the intensity of the symptoms may decrease or even disappear over the course of the summer months.^[2] If people affected by sun allergy avoid the sun, the rash may disappear within two weeks without scarring; however, sun allergy symptoms may return or even spread if that person re-exposes themselves to sunlight – especially if they do so before the rash has cleared up.^[13]

Did you know that a sun rash can develop through thin clothing and if you’re sitting close to a window?^[13]

A sun rash caused by polymorphous light eruption can easily be mistaken for other common summer skin conditions. A common error made is confusing a sun allergy with prickly heat – also known as a heat rash. This is also a skin condition that typically becomes problematic in summer.

Sun allergy versus prickly heat: what’s the difference?

Polymorphic light eruption is often mistaken for prickly heat, another skin condition that emerges with the arrival of hot summer days. Unlike polymorphous light eruption – that is, a sun allergy – prickly heat is caused by warm weather or overheating, not by sunlight or UV light.^[13]

Skin affected by prickly heat does not tend to acclimatise to the environment, as is the case for polymorphic light eruption.

What are other skin conditions that emerge in summer?

Another uncomfortable but much more common skin condition that people with sensitive skin need to be wary of is sunburn. With sunburn, redness, sensitivity to touch and pain occur during sunbathing or a few hours afterwards. The sunburn then develops continuously after sun exposure and then starts healing again after 12 hours through the skin peeling.^[3]

Typical skin reactions between sun allergy and sunburn include:^{[1, 2, 4]} 

Skin reactions to sun allergy	Skin reactions to sunburn
Varies from person to person, usually itchy in the form of: – Patchy red rashes on the skin (erythema) – Raised and hardened nodules on the skin (papules, welts) – Blisters	– Reddening of the skin – Swelling – Itchiness – Pain – In rare cases, blisters

 

Mallorca acne, also known as acne aestivalis, is a skin condition similar to polymorphous light eruption. However, the trigger of this skin condition is a reaction between the UV radiation of the sun and the fat components of suncreams and the body’s own sebaceous oils.^[5] In most cases, it is sufficient to switch to suncreams or lotions that are free of fats and emulsifiers.^[6]

What are typical sun allergy causes?

What exactly causes an allergic reaction due to UV exposure is not known. Researchers suspect the reaction takes place due to the body’s own substances or free radicals in the skin.^[4] The skin becomes inflamed as a result of this reaction to UV light. In central Europe, 10 to 20 per cent of the population is affected by sun allergy.^[8]

Sun allergy can appear for the first time during childhood or adulthood around the age of 20 – but symptoms can usually emerge up to the age of 40. This seasonal skin condition can run in families; around one-fifth of people with a sun allergy has a relative who also suffers from a sun allergy.^[13] 

People with fair skin are particularly affected, and women are especially frequently affected. In fact, women suffer from sun allergy more than twice as often as men.^{[1, 2, 13]}

How do UVA and UVB radiation affect the skin?

People affected by a sun allergy mostly react to a very specific UV wavelength range – the action spectrum.^[4] Ultraviolet (UV) sunlight can be differentiated by its wavelengths into UVC, UVB and UVA radiation. The shorter the UV wavelength, the greater and more damaging the radiation. UVC radiation has a short wavelength of 100 to 280 nanometres, but it never reaches the earth’s surface and is therefore not responsible for skin conditions.^[7]

UVB radiation is in the medium-wave range with radiation of wavelengths spanning 280 to 315 nanometres. UVB radiation is particularly responsible for sunburn and long-term effects such as skin ageing or skin cancers at prolonged or high UV doses – which can affect anyone.

UVA radiation is in the wavelength range of 315 to 400 nanometres and is the main trigger of a sun allergy, which does not affect everyone. Around 80 per cent of sun allergy sufferers react to UVA radiation and ten per cent to UVB radiation or a combination of UVA and UVB radiation.^[1] UVA radiation can also penetrate glass and trigger skin reactions through light exposure through a closed window.^[8]

Fifty per cent of the UVB radiation that causes skin reactions is present between 11 a.m. and 1 p.m. Especially during this time, make sure you use sufficient suncream, wear protective clothing and stay in the shade, if possible.^[9]

But is UV good for skin?

As much as you need to protect your skin from UV radiation, you equally need to make sure that you receive enough vitamin D during the sunny months – otherwise, you risk developing a vitamin D deficiency. Vitamin D, also known as the ‘sunshine vitamin’, can only be produced in your body with UVB rays – which can’t pass through glass if you’re sitting near a window when the sun is shining.

Maintaining optimal vitamin D levels ensures that you boost your bone health, strengthen your immune system and lift your mood. We can optimise our vitamin D levels through exposing our skin to the sun, through eating food rich in vitamin D or by taking vitamin D supplements.

In the United Kingdom, we receive most of our vitamin D between late March and the end of September by exposing parts of our body, such as our forearms, hands and legs, to the sun.^[14] How long you need to stay in the sun to ensure the production of vitamin D in your body varies from person to person. The most important thing is that you avoid spending too long in the sun without adequate sun protection! 

Did you know that people with darker skin need to expose themselves to more sun than those with fairer skin in order to produce the same amount of vitamin D in their bodies?^[14]

Does sun tan lotion block vitamin D?

There is no evidence to suggest that wearing suncream to protect yourself from UV rays in our environment inhibits you from absorbing your necessary vitamin D. High-SPF suncreams filter out the majority of UVB radiation; however, even with all the protection that such products offer, some of this radiation will reach your skin. There are furthermore far more proven benefits of wearing suncream while you are exposed to the sun, such as significantly reducing the risk of skin cancer.

How is vitamin D linked with polymorphous light eruption?

Those affected by polymorphic light eruption are at a higher risk of developing a vitamin D deficiency, as they may tend to avoid sun exposure to relief or prevent sun allergy symptoms. This sun exposure is, however, necessary in order for our bodies to produce its own vitamin D.^[13]

If you are concerned about your vitamin D levels and do not wish to or are unable to expose your skin to sufficient sunlight – perhaps due to a sun allergy – you can check your vitamin D levels with at-home vitamin D test kits, or you can discuss taking vitamin D supplements with a doctor.

Are there other skin reactions to sun exposure?

Skin reactions triggered by UV radiation can be triggered by certain substances – namely, by photosensitisers. This is known as a secondary reaction, since the skin does not only react to solar radiation, but other factors also play a role in the reaction. There are about 400 known substances that can trigger a skin reaction in connection with sun exposure.^[8]

This type of secondary reaction is divided into photoallergic and phototoxic reactions. Anyone can be affected by a phototoxic reaction, whereas a sensitivity must be present for a photoallergic reaction. A reaction triggered by a photosensitiser can be more severe and appear more quickly.^[8] In particular, phototoxic reactions can be very extensive, usually resulting in blisters and sunburn-like symptoms.^[10]

Topical versus systemic photosensitisers

‘Topical’ refers to products manufactured for external application. In particular, non-steroidal anti-inflammatory drugs and some suncreams, which paradoxically are supposed to protect against the sun, can cause skin reactions when it is exposed to the sun. In this case, skin reactions mostly only appear in areas of the skin that have come into contact with the topical photosensitiser. When using sunscreen, be sure to check the ingredients. Ideally, choose a suncream with inorganic micropigments. However, the best protection from UV exposure is clothing.

Systemic photosensitisers are substances that are absorbed into the body and can promote sun sensitivity. The sensitising substance enters the skin via the bloodstream and then causes a skin reaction combined with UV irradiation.

Typical systemic photosensitisers include:^[8]

• Antibiotics such as tetracyclines and sulphonamides
• Antirheumatic drugs
• Antihypertensive drugs
• Drugs for dehydration (diuretics)
• Cell-damaging drugs (cytostatics)
• Certain psychotropic drugs

If you suspect that you are having a photoallergic or phototoxic reaction caused by photosensitisers, doctors can identify the cause by means of a prick test with the suspected substance, followed by subsequent irradiation with UV light.^[8]

Who do I know I have a sun allergy?

A sun allergy is mostly diagnosed by photoprovocation. In this procedure, different areas of the skin are irradiated with UV light to trigger a reaction. If a skin reaction triggered by photosensitisers is suspected, a photopatch test is performed, in which skin areas treated with test substances are irradiated and compared.^[4] A sun allergy diagnosis is then made if the same skin changes repeatedly occur after UV exposure of the skin.^[2]

What is the best sun allergy treatment?

Unfortunately, you can’t cure polymorphic light eruption, but you can relieve symptoms by using high-quality suncreams and avoiding too much sun exposure. You should avoid the sun when it is at its strongest – that is, between 11 a.m. and 3 p.m. in the warmer months. Wear protective clothing and stay in the shade, where possible.^[13]

You should also avoid identified photosensitisers – however, medicines should not be discontinued without first consulting your doctor. If you allow your skin to slowly get used to sun exposure, you may find your sun allergy symptoms improve.

What if I have acute sun allergy symptoms?

Your doctor will usually prescribe a cream or gel with an anti-allergic effect to be applied to the affected areas of the skin to relieve the symptoms. In particularly severe cases, cortisone may be prescribed for application or ingestion.^{[2, 4]}

Sun allergy treatment: which supplements and medication?

Besides suncreams and lotions, medications can also help as sun allergy treatment. For example, taking beta-carotene, calcium, nicotinamide or folic acid at the beginning of the summer can help people slowly get used to sun exposure.^[6] In addition, a medicine based on the South American fern plant Polypodium leucotomos is said to be an effective addition to suncream products.^[2]

Did you know that omega-3 fatty acids and probiotics are said to be able to alleviate irritated skin? However, the extent to which they can have a positive effect on skin has not yet been scientifically proven.^[4] Read more about the benefits of omega 3 and omega 6 in our online Health Portal article.

How can hardening help treat polymorphic light eruption?

The habituation effect achieved by slowly getting used to UV radiation is the idea behind the medical light-hardening method. 

‘Hardening’ in this context means that the skin becomes more resistant to sun exposure. Dermatologists irradiate patients with UVB light from special devices, so that patients slowly develop resistance to UV light over time.

This sun allergy treatment takes place several times a week over several weeks – usually in spring. This hardens the skin for a certain period of time. However, this sun allergy treatment must be repeated every year, as protection wears off during winter months, when sun exposure is less frequent.^[1]

Hardening should only be carried out by trained professionals and not on a sun bed, as UV exposure should be kept as low as possible.^[9]

How do you treat sun allergy in children?

Compared with adults, children are rarely affected by sun allergy, as skin reactions usually develop in early adulthood. According to study findings, photosensitisers very rarely play a role in polymorphous light eruption in children.^[11]

However, it is important to ensure that children use adequate sun protection and only receive low levels of direct UV radiation. They should be taken to a dermatologist if they do suffer from skin reactions. This can reduce the chance of sunburn and other skin diseases as well as the risk of skin cancer.^[11]

DNA analysis: how can I check my skin type at home?

Certain DNA home test kits can analyse your saliva for specific genes. These genes provide you with great insights into your skin, such as collagen degradation, your risk of oxidative stress and even your sensitivity to the sun. More importantly, with this information, you can boost your skin health and slow down the negative effects of UV exposure.

A genetic predisposition can possibly cause some people to react more sensitively to UV radiation – whether this manifests itself in a sun allergy or not. Skin damage is more likely to occur among such people. This is why it is often interesting to gain more insights into your skin type – and a better idea of how to keep your skin healthy and happy.

Sun allergy symptoms and treatment – at a glance

What is a sun allergy?

A sun allergy is an allergic reaction of the skin triggered by UV radiation. This can be triggered either by the interaction of skin and UV radiation or by a sensitising substance.

What are typical sun allergy symptoms?

Skin reactions can vary from person to person. In the hours to days following UV exposure, itchy skin changes form in the form of a sun rash, welts, nodules or blisters.

How can I prevent a sun allergy reaction?

Avoid direct sun exposure or identified photosensitisers. Also, use sufficient UV protection and clothing and consult your doctor about protective medicines or hardening treatment.

Sources

^[1]       ‘Sonnenallergie’, available at https://www.daab.de/haut/sonnenallergie/, accessed on 11 May 2021.

^[2]        Abeck, D. Häufige Hautkrankheiten in der Allgemeinmedizin. Springer, 2010.

^[3]        Smolle, J., Mader, F. H. Beratungsproblem Haut. Springer, 2005.

^[4]        Zuberbier, T. ‘Sonnenallergien’, Allergieinformationsdienst – Helmholtz Zentrum München – Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/krankheitsbilder/sonnenallergien.html, accessed on 10 May 2021.

^[5]        A.-M. D. A. GmbH, ‘Polymorphe Lichtdermatose: Sonnenallergie, die vielleicht keine ist’, Pharmazeutische Zeitung online, available at https://www.pharmazeutische-zeitung.de/ausgabe-222012/sonnenallergie-die-vielleicht-keine-ist/, accessed on 10 May 2021.

^[6]       ‘Sonnenallergie ist keine echte Allergie auf Sonne’, available at https://www.aeda.de/presse/pressearchiv/einzelansicht/?tx_ttnews%5Btt_news%5D=141&cHash=b8c7b142710961d4129dcd8ba365bb0e, accessed on 10 May 2021.

^[7]       ‘Was ist UV-Strahlung?’, Bundesamt für Strahlenschutz, available at https://www.bfs.de/DE/themen/opt/uv/einfuehrung/einfuehrung_node.html, accessed on 10 May 2021.

^[8]        Wilm, A., Berneburg, M. ‘Photoallergie’, JDDG: Journal der Deutschen Dermatologischen Gesellschaft, vol. 13(1), pp. 7–13, 2015.

^[9]        Thomas, P. ‘Lichtdermatosen’, in Therapie der Krankheiten im Kindes-und Jugendalter, Springer, 2014, pp. 1121–1123.

^[10]      Wiesner, T., Smolle, J., Fried, I., Sterry, W., Kerl, H. Das Derma-Kurs-Buch: Fallbezogenes Lernbuch zur Dermatologie, Allergologie und Venerologie. De Gruyter, 2012.

^[11]      Fauziah, S. N., Indriatmi, W., Legiawati, L. ‘Photodermatoses in children’, Journal of General-Procedural Dermatology and Venereology Indonesia, pp. 77–88, 2017.

^[12]     ‘UV-Schutz durch Sonnencreme’, Bundesamt für Strahlenschutz, available at https://www.bfs.de/DE/themen/opt/uv/schutz/sonnencreme/sonnencreme_node.html, accessed on 10 May 2021.

^[13]      ‘Polymorphic light eruption’, National Health Service, available at https://www.nhs.uk/conditions/polymorphic-light-eruption/, accessed on 27 May 2021.

^[14]      ‘How to get vitamin D from sunlight’ National Health Service, available at https://www.nhs.uk/live-well/healthy-body/how-to-get-vitamin-d-from-sunlight/, accessed on 27 May 2021.

^[15]        Fritsch, P. ‘Aufbau und Funktionen der Haut’, in Dermatologie Venerologie, Berlin, Heidelberg: Springer Berlin Heidelberg, 2004, pp. 3–42.

^[16]      DeWeerdt, S. ‘The edible skincare diet’, Nature, vol. 563(7732), pp. S94–S95, Nov. 2018, doi: 10.1038/d41586-018-07433-7.

^[17]      Schagen, S. K., Zampeli, V. A., Makrantonaki, E., Zouboulis, C. C. ‘Discovering the link between nutrition and skin aging’, Dermatoendocrinol, vol. 4(3), pp. 298–307, July 2012, doi: 10.4161/derm.22876.

^[18]      Boelsma, E., Hendriks, H. F., Roza, L. ‘Nutritional skin care: health effects of micronutrients and fatty acids’, Am J Clin Nutr, vol. 73(5), pp. 853–864, May 2001, doi: 10.1093/ajcn/73.5.853.

^[19]      Nagata, C. et al., ‘Association of dietary fat, vegetables and antioxidant micronutrients with skin ageing in Japanese women’, Br J Nutr, vol. 103(10), pp. 1493–1498, May 2010, doi: 10.1017/S0007114509993461.

^[20]      Cosgrove, M. C., Franco, O. H., Granger, S. P., Murray, P. G., Mayes, A. E. ‘Dietary nutrient intakes and skin-aging appearance among middle-aged American women’, Am. J. Clin. Nutr., vol. 86(4), pp. 1225–1231, October 2007, doi: 10.1093/ajcn/86.4.1225.