Definition
Strong sunlight can cause skin rashes. Many people suffer from rashes especially in spring and at the beginning of summer when the first stronger sunrays hit the skin. In general, all changes in the skin caused by ultraviolet or visible sun rays are called photodermatoses.
These include relatively harmless rashes and more serious skin diseases. It is not a uniform clinical picture, but a collective term that covers various diseases. According to the ICD-10 (international classification system of diseases), the following diseases are summarized under the term “photodermatoses”: The symptomatology of the diseases is different.
Skin rashes caused by sun exposure are usually understood to be acute sunburns (Dermatitis solaris) or the polymorphic light dermatosis, which is often, admittedly but erroneously, called light allergy or sun allergy. However, phototoxic or photoallergic dermatoses, which also cause skin rashes due to the sun, must also be mentioned. Here, drugs or other substances can lead to an increased light sensitivity of the skin and thus to skin rashes.
- Phototoxic reaction to drugs
- Photoallergic reaction to drugs
- Phototoxic contact dermatitis
- Uriticaria solaris
- Polymorphic light dermatosis
- Other acute skin changes caused by ultraviolet rays
- Acute skin changes caused by ultraviolet rays, not specified
Causes
The causes of skin rashes caused by the sun are very different. This is due to the fact that the sun’s rays can cause very different skin symptoms. In the following section, the most important causes and clinical pictures will be briefly presented so that a distinction can be made.
- Sunburn (Dermatitis solaris): A possible cause of a skin rash caused by the sun is dermatitis solaris, which is commonly known simply as sunburn. The sunburn is similar to a first to second degree burn of the skin. It is a radiation-induced damage to the upper skin cells (epidermis cells).
This leads to reddening and swelling of the skin with blistering. This usually heals without scarring, but can also leave light scars. The cause of sunburn is the UV radiation of the sun.
- Polymorphic light dermatosis (sun allergy): Polymorphic light dermatosis is the change of the skin, which is commonly known as light or sun allergy.
However, this term is incorrect, as it is not an allergic reaction of the skin. The cause of polymorphic light dermatosis is unknown. Usually hours to days after the first contact with sunlight after the winter months, a skin rash appears, which is characterized by a blotchy appearance.
Reddening and blistering occurs. In addition, severe itching is characteristic. However, the appearance of the skin varies from patient to patient.
It is interesting, however, that each patient with a new light dermatosis has the same skin changes that he/she suffered before. One hypothesis for the development of polymorphic light dermatosis is that UV exposure produces antigens in the body, against which a defense reaction then occurs.
- Photosensitivity: The term photosensitivity describes a pathological sensitivity of the skin to light. It can have many different causes.
These can be drugs, substances or even metabolic diseases that make the skin susceptible. The skin reacts to even the slightest exposure to light or sunlight with rashes, redness, itching, burning, sensation problems or sunburn. Photosensitivity occurs, for example, in the disease Xeroderma Pigmentosum.
- Photoallergic Dermatitis: Photoallergic dermatitis is a disease that causes an allergic reaction of the skin.
It is caused by the combination of UV (A) radiation and a specific substance that has previously sensitized the skin. Such a substance can be, for example, a drug or a dye. Fragrances or ingredients of sunscreens are also common allergens.
The skin symptoms are then limited to the areas exposed to light. At the same time, these skin areas must also have had contact with the allergen. Redness and papules appear, less frequently blisters appear.
- Lupus erythematosus: Lupus erythematosus is an autoimmune disease associated with increased sensitivity to light.
It leads to typical skin symptoms, which include the so-called butterfly erythema of the face. This is so called because of its typical shape. Lupus erythematosus represents a complex clinical picture in which other internal organs, such as the heart or kidney, are involved.
The cause is the production of antibodies against the body’s own cell components.
- Rarer causes: There are some rarer diseases that can lead to skin rashes from the sun. Here too, allergens and skin sensitization play a decisive role. One example of such a rarer skin rash caused by the sun is water grass dermatitis.
Contact of the skin with certain components of the plant and subsequent UV-A radiation from sunlight leads to a stripy to net-like rash. This reaches its maximum after 3 days with reddening and blistering. The rash only appears on those parts of the skin that have had contact with the plant.
After 2 to 4 weeks the rash heals. However, over-pigmentation may remain on the skin for months, visible as darker areas. Another rare cause is Berloque dermatitis, also called photodermatitis pigmentaria.
This is also a phototoxic dermatitis. It is caused by plant substances, which are often contained in perfume, in combination with sunlight on the skin. An increased pigmentation of the skin is typical here.
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