Sun allergy refers to different types of pathologies that affect the skin and that are related to a hypersensitivity in which the immune system intervenes, that is, it is not the sun that causes allergies, but rather different skin reactions that They need sun exposure to develop. They are popularly known as “sun allergy” but, really, it is not the correct clinical term. They are photodermatoses.
The signs and symptoms of the so-called sun allergy depend on the type of photodermatosis. The most common are photodermatoses of spontaneous irruption or unknown cause (idiopathic):

Polymorphous solar eruption:It affects more women than men with fair skin (phototype I/IV). It can appear from childhood to, in general, the 30 years. They usually have a family history. It appears characteristically in the spring and fades as the sunny and hot months progress. Lesions appear on the skin, usually on the chest, (papules, papulovesicles, plaques, vesiculoblisters or eczema), although it is true that it may only feel itchy. Lesions that occur between 30 minutes from the start of sun exposure to several hours later. These lesions disappear between one and seven days later without leaving a scar.

Actinic prurigo:It usually appears between the ages of five and ten, especially in girls, and disappears at puberty. Patients usually have a family history. Actinic prurigo presents with a rash that can last all year but worsens in summer. It presents as open (excoriated) papules and nodules, very pruritic and usually with eczema, lichenification and crusting.

Chronic actinic dermatitisincludes photosensitive eczema, actinic reticuloid, persistent reactivity to light and photosensitivity dermatitis: It has an insidious onset. It is most often diagnosed in older men and begins with itching of the face, neck, and backs of the hands. The itching evolves into eczematous lesions, papules and infiltrated patches that may appear in exposed areas but later appear in areas normally covered by clothing.

Hydroa vacciniforme of Bazin: It is very infrequent and usually appears in children up to ten years of age with clear phototype I/II. Often coexists with atopic dermatitis. Erythema appears, usually on the face, after long sun exposure that evolves into vesiculoblisters and leaves scars when healed. There may be fever and malaise.

Photosensitization by chemical substances (exogenous or endogenous): porphyrias, photoallergy and photosensitivity: lesions compatible with an exaggerated sunburn appear, without proportion between the intensity of sun exposure and that of the lesions. In the area exposed to the sun there may be erythema, edema, vesicles, blisters, hyperpigmentation, burning, itching and itching. If the cause is photoallergic, eczematous plaques appear with scaling and vesiculoblisters of insidious onset and itching.


Treatment should be appropriate to the type of photodermatosis:
– Polymorphic solar eruption: Avoid sun exposure and use broad-spectrum sunscreens. In severe cases, low-dose prophylactic photochemotherapy may be considered. In patients in whom the rash is not controlled with these measures, a topical treatment with corticosteroids or a short course of oral corticosteroids will be prescribed.
– Actinic prurigo: It is recommended to cover the skin, avoid sun exposure and use broad-spectrum photoprotectors. Thalidomide is also prescribed in intermittent cycles at low doses.
– Chronic actinic dermatitis: Total screen photoprotectors and low allergenic potential are prescribed.
– Solar urticaria. Treatment is based on avoiding exposure to the sun and using broad-spectrum photoprotectors. To help habituate the skin (hardening phenomenon), a month before, a treatment of oral antihistamines and beta-carotene can be prescribed.
– Hydroa vacciniforme of Bazin: It is very infrequent and usually appears in children up to the age of ten. It usually coexists with atopic dermatitis. Sun exposure should be avoided and prophylactic photochemotherapy is usually considered in some cases.
-Photosensitization by chemical substances (exogenous or endogenous): Eliminating the substance that causes the symptoms is the main treatment, although a possible chronification should be monitored. Sunscreens do not protect against photosensitization by chemical substances. For example, if antibiotic treatment is followed, sun exposure should be avoided during treatment and up to three days after completion.

Prevention of sun allergy

Use sunscreens that protect the skin from sun exposure, appropriate to the type of skin and state of health; and avoiding sun exposure, even with clothing that covers arms and legs as well as hats, are the main preventive measures against a possible photodermatosis.
It is also important to remember that if you are on antibiotic treatment you should not sunbathe or be exposed to direct sunlight during treatment and for three days after completion.

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