They are popularly known as “Sun Allergy” but it really is not the correct clinical term, that is photodermatosis. It is a group of cutaneous diseases that have pathological photosensitivity as a primary symptom or phenomenon. Photosensitivity is an abnormal reaction to ultraviolet radiation. The most common are acquired idiopathic photodermatoses, of spontaneous eruption or unknown cause, such as polymorphic solar rash.

Causes of Sun Allergy

Abnormal reaction to Ultraviolet Radiation

Photodermatoses, popularly known as allergies to the sun, caused by an abnormal reaction to ultraviolet radiation can be:

Acquired idiopathic photodermatoses such as: Solar polymorphous rash, Actinic prurigo, Bazin’s vacciniform hydroa, Solar urticaria or Chronic actinic dermatitis (photosensitive eczema, actinic reticuloid, persistent light reactivity and photosensitivity dermatitis). Chronic actinic dermatitis is believed to have an immune basis.

Disorders due to defective DNA repair such as: Xeroderma pigmentosum , Bloom syndrome or Cockayne syndrome.

Photosensitization by chemical substances (exogenous or endogenous): Porphyrias, Photoallergies and Photosensitivity. They can be associated with the same drugs such as: antiarrhythmics, contraceptives, anticonvulsants, antihypertensives, oral antidiabetics, antiparasitics, psoralen, cytostatics, antidepressants, diuretics, antipsychotics, antihistamines, non-steroidal and / or antimicrobial anti-inflammatory drugs.

Dermatoses exacerbated by ultraviolet radiation such as: Acne vulgaris, Carcinoid syndrome, Dermatomyositis, Disseminated superficial actinic prorokeratosis, Lichen planus, Lupus erythematosus, Pellagra, Rosacea , Flat warts, Pityriasis alba or Haley-Haley disease.

Solar urticaria. It is an immunoglobulin E (Ig E) mediated type 1 hypersensitivity reaction. It is very rare and usually appears, especially in women, between the ages of 20 and 40. It starts with itching and erythema and in a few minutes there are hives in photo-exposed areas such as the face and hands that disappear in an hour or two, and do not leave a scar, avoiding exposure to the sun.

Sun Allergy Symptoms

Depend on the type of Photodermatosysis

The signs and symptoms of so-called sun allergy depend on the type of photodermatosis. The most common are spontaneous irruption or unknown cause (idiopathic) photodermatoses:

Solar polymorphous rash: It affects more women than light-skinned men (phototype I / IV). It can appear from childhood to, usually, 30 years. They usually have a family history. It characteristically occurs in spring and dims as the hot, sunny months progress. Lesions appear on the skin, usually the chest, (papules, papulovesicles, plaques, vesicles, blisters or eczema ), although it is true that you can feel only itching. Lesions that occur between 30 minutes from the start of sun exposure to several hours later. These lesions disappear one to seven days later without scarring.

Actinic prurigo: It usually appears between the ages of five and ten, especially in girls, and disappears at puberty. Patients often 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 itchy and, usually, with eczema, lichenification and crusts.

Chronic actinic dermatitis includes photosensitive eczema, actinic reticuloid, persistent light reactivity and photosensitivity dermatitis: It has an insidious onset. It is most frequently diagnosed in older men and begins with itchy face, neck, and back of the hands. The itch progresses to eczematous lesions, papules and infiltrated bales that can appear in exposed areas but later appear in areas normally covered by clothing.

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

Photosensitization by chemical substances (exogenous or endogenous): porphyrias, photoallergies and photosensitivity: Lesions compatible with an exaggerated sunburn appear, with no 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, stinging and itching. If the case is photoallergic, eczematous plaques appear with peeling and blistering with an insidious onset and itching.

Diagnosis of Allergy to the Sun

Physical Exam, Medical History and Tests

The doctor will need to know the family history, the usual or recent treatments that the patient follows or has followed, how the disease began, what is its evolution and the previous history of photo-exposure, as well as the cutaneous response to sunscreens.

In addition, it will request a complete blood test, blood biochemistry, antinuclear detection (ANA), antibodies (anti DNA, anti Ro and anti LA), porphyrins in urine and blood, and biopsy with immunofluorescence.

It is key to make a differential diagnosis to be able to conclude on the type of photodermatosis that affects the patient and to be able to apply the appropriate treatment.

Sun Allergy Medication and Treatment

Suitable for the type of Photodermatosis

Treatment must be appropriate to the type of photodermatosis:

Polymorphic sun rash: 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, 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 sunscreens. Thalidomide is also prescribed in intermittent cycles at low doses.

Chronic actinic dermatitis: Full screen photoprotectors with low allergenic potential are prescribed.

Solar urticaria. The treatment is based on avoiding sun exposure and using broad-spectrum sunscreens. To help skin habituation (hardening phenomenon) one month before, an antihistamine and beta-carotene treatment can be prescribed orally.

Hydroa vacciniforme de Bazin: It is very rare and usually appears in children up to ten years of age. It usually coexists with atopic dermatitis . Avoid sun exposure 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 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 the treatment and up to three days after the end of the treatment.

Prevention of Allergy to the Sun

Sun Protection and Avoid Sun Exposure

Use sunscreen that protects the skin from sun exposure, appropriate to the type of skin and the 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 possible photodermatosis.

It is also important to remember that if an antibiotic treatment is followed, you should not sunbathe or be exposed to light alone during the treatment and up to three days after the end of it.