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Sun allergy: polymorphic or polymorphous light eruption

sun allergy solar urticaria polymorphic polymorphous light rash
Sun Allergy

Sun allergy and polymorphous rash: 6 details to know

  1. Its medical name is “photodermatosis”
  2. It is a very common disease and can be present in up to 10-20% of the population.
  3. Most cases are mild and do not require treatment.
  4. There is no single disease called a sun allergy, but the sun can cause many skin conditions.
  5. The most common sun allergy is polymorphous light eruption
  6. All of them improve knowing when the patient knows how the disease works.

Dr Tito Rodriguez Bouza

Know the causes of your disease as well as the rationale for your treatments, without leaving home, asking for an in-depth and quality consultation

Sun allergy


Explanatory note: in this article the term sun allergy is used for ease of the patient but it is more correct to speak of photodermatosis. (Photo = light, derma = skin, -osis = disease)

Although there are many types of allergy to the sun or photodermatoses, in this article we will only focus on the two most frequent: the polymorphic light and solar eruption. Additionally, the drugs we take can also cause a sun allergy and should be checked up.

Why does Allergy to the sun occur?

Actually, we don’t know exactly what causes photodermatoses. In the case of the two most frequent allergies to the sun, such as the polymorphous solar rash and solar urticaria, if we simplify what we know so far, it can be said that there are multiple studies that indicate in the direction that these reactions can This is due to the changes that the sun produces in certain proteins of the skin and that such proteins, when modified, are recognized by the defense system of our body as foreign, thus producing the reaction in the skin.

In fact, there are studies that take samples of our own skin and they expose it to our own cells in the laboratory, and a reaction only occurs when skin samples have been previously exposed to ultraviolet radiation.

What does seem clear is that the sun in one way or another activates two mechanisms, one predominant in the polymorphic light eruption that depends on cells called lymphocytes, which require hours to be activated and produce an accumulation of cells and substances that explain the red and hardened lesions that patients present, and another predominant in solar urticaria that depends on cells called mast cells, which can become activated in seconds, and that release, among others, a protein called histamine which is capable of being produced by itself itchy redness and hives of the skin. Both mechanisms can occur together in both diseases, although one predominates over the other.


¿What is solar Urticaria?

Urticaria is the presence of itching, pruritus or itching along with redness of the skin, hives disappearing or changing the location of the lesions typically within 24 hours. The “sun allergy” known as solar urticaria is therefore the one that occurs when the patient is exposed to the sun

What symptoms does solar urticaria give?

The typical urticarial lesions, such as those seen in the photo below, & nbsp; They usually start as itching and redness progress over time and exposure until the development of hives. They usually start from 2-3 minutes of exposure to sunlight in areas of skin that are not sufficiently covered.

When the patient stops being in the sun, symptoms typically disappear in less than 24 hours. If, on the other hand, the patient continues to be exposed, the symptoms will worsen, with rare cases of serious allergic reactions when the exposure is intense and prolonged.

sun allergy solar urticaria polymorphic polymorphous light rash
Solar urticaria

How is solar urticaria diagnosed?

For this type of allergy to the sun, a complex diagnostic test is not necessary since the patient’s symptoms after exposure to the sun are usually quite clear, a good quality photograph being enough for the diagnosis.

How is solar urticaria treated?

Antihistamines and protection against the sun are the basis of treatment. Treatment must be specific for each patient since the doses will depend on the number of symptoms. In addition, a combination must be found that does not cause the typical side effects of antihistamines, among which drowsiness stands out. Not all patients will release the same amount of histamine and therefore the treatment dose is not the same for all.

Severe cases where the initial treatment is not effective should be referred to your dermatologist, who may consider the ultraviolet light therapy


What is polymorphic light eruption?

It can be called both as polymorphic or polymorphous light eruption and It is undoubtedly the most frequent reaction to the sun, affecting up to 20% of the population in some countries, being up to four times more frequent in women and occurring in countries with hot climates. In fact, the accompanying photos correspond to Dr. Tito Rodriguez Bouza’s own mother when she started with this ailment.

When a patient says he has an allergy to the sun, in most cases it is this condition, and consists of lesions that can be from small pimples and vesicles that produce itching.

The polymorphic light eruption produces lesions that, as its name suggests, can have multiple forms (Poly = multiple, morph = form) and appear hours or days after exposure to the sun, with symptoms lasting for days. Among the forms of this include itchy lesions (itching, pruritus or itching) in the form of plaques, insect bites, pimples or pimples with small vesicles. These lesions, unlike solar urticaria, do not resolve in 24 hours but in several days.

sun allergy solar urticaria polymorphic polymorphous light rash
Polymorphous light eruption ( Courtesy of Magdalena Bouza )

Why does it not affect hands and face?

In this form of allergy to the sun, the polymorphous light eruption, the areas that are repeatedly exposed paradoxically present a process called “hardening” by which they progressively get used to it and therefore fewer symptoms appear, the reason being that being continually exposed face and hands, significant symptoms in these locations no longer develop over time. If you suffer from this disease you will have noticed that at the end of the summer you have less problems than at the beginning of the summer, and this is due to the hardening process.

How is polymorphous light eruption treated?

For this type of allergy to the sun, it is important that the patient knows the causes of his illness, because only in this way can it be treated. Prevention in this case is more important than treatment itself.

Treatment should always include creams that have the highest sun protection factor. In addition, it is advisable to enhance the hardening that we talked about in a previous section. Other measures with drugs must be evaluated by the responsible doctor to find a correct combination.

In addition, it should not be forgotten that polymorphous light eruption patients tend to take less sun and this can affect their bones, so this aspect must be reviewed, as well as providing treatments such as vitamin D, which can also be provided by itself. protect against disease.

Your doctor should also consider the introduction of certain vitamins that can also protect against sun damage.

In severe cases of polymorphous light eruption that do not respond to previous treatments, the ultraviolet light therapy , this therapy should be supervised by a dermatologist.

8 thoughts on “Sun allergy: polymorphic or polymorphous light eruption”

  1. According to my Doc.In allerchology,my allery is extremely hot and cold.or call Climate.I,have a shot for every 3 month for my allergies now I’m looking a nearest hospital for my shot.near bulacan city.at this time pandemic it’s very hard to travel.

      1. we just come in philippines for vacation right now and 2 days when we arrived hives shows up i notice it comes back after expose in the sun. i need a consultation si bad for him please let me know how can i contact u

  2. I have a pretty bad rash I don’t know what is it, I’m desperate I can’t tolerate the itch anymore it’s all over my legs and arms. I can’t even sleep. Heeelp

      1. Dear doctor,
        My partner had 3 months of light therapy, and his skin was clear.
        2 weeks after he began to get small spots coming up.
        Another week later) at this moment) we went to Aruba, he sits in the sun to get his skin calm (was calm yesterday) but today his legs have an outburst worst than I have ever seen. I think he should go to a hospital, like an acute sun allergy I sint know. He keeps sitting in the sun hoping it gets away, please help.

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