Symptoms
Within minutes to hours or days, a red and itchy to burning rash appears after exposure to UV radiation (sunlight, solarium). It manifests itself in numerous forms, including papules, vesicles, papulovesicles, small blisters, as eczema or plaque, and is therefore called polymorphic. However, the same expression is usually observed in individual patients. Most affected are sun-exposed skin areas such as the neck and chest, the extensor sides of the arms, the backs of the hands, the legs, the neck, and possibly the face and ears. A sun allergy occurs chronically recurring mainly in spring to summer and more often in women. The rash disappears within a few days to a week without scarring if the triggers are avoided. Habituation usually develops during the summer.
Causes
Trigger is UVA and/or UVB radiation (sun, solarium). UVA is often exclusively blamed for the rash, but UVB may also be involved. The underlying cause is still not precisely understood. An immunological cause is suspected, as the disease resembles a cell-mediated immune response of the delayed type. According to a common hypothesis, an endogenous antigen is formed by UV radiation, which triggers an allergic reaction. Normally, the skin is protected from such antigens because UV radiation suppresses the immune response. Therefore, a lack of immunosuppression could also play a role. The formation of an endogenous photosensitizing substance has also been discussed.
Diagnosis
The diagnosis is made under medical treatment on the basis of the clinical presentation and patient history and possibly additionally on the basis of a provocation test with UV light. Possible differential diagnoses include other photodermatoses such as solar urticaria, actinic prurigo, Majorca acne, lupus erythematosus, and other skin diseases.
Prevention
For prevention, it is recommended to avoid sun exposure, sunbathing and solarium visits. A good sunscreen with UVA and UVB filters, with a protection factor above 30 adapted to the skin type and as high as possible should be applied as a preventive measure. In severe cases, phototherapy with UVA, UVB or PUVA is possible under medical treatment. With progressive exposure, this results in thickening and tanning of the skin and thus in “hardening”. The following substances, among others, are used for medicinal prevention. Their effectiveness has not been clearly proven scientifically: Beta-carotene, calcium, folic acid, nicotinamide (controversial), vitamin E, omega-3 fatty acids and hydroxychloroquine. Since these agents, except hydroxychloroquine, are well tolerated, preventive use can be tried, provided there are no restrictions on use and no interactions with other drugs. The antimalarial drug hydroxychloroquine has a photoprotective effect by reducing the sensitivity of the skin to UV radiation and is approved as a drug in this indication.
Drug treatment
The anti-inflammatory, immunosuppressive, and antiallergic glucocorticoids are used in medical treatment of acute light dermatosis. They can be applied internally and/or externally. In self-medication, the weakly effective hydrocortisone is available. Further, antipruritic agents, topical and oral antihistamines, and less frequently immunosuppressants are used. Skin care products such as hydrolotions, creams, and foam sprays can provide symptomatic relief. Alternative medicines such as cardiosperm ointments are also commercially available. The efficacy of drug treatment has not yet been reliably demonstrated.
