Sun allergy or solar urticaria

Not all the reactions manifested after the exposition to sunlight are of an allergic type, most of them are an effect of the action of sunlight over the skin (like simple burnings or irritating actions), according to the opinion of experts. The real allergy to sun comprises only those disorders on which the immune system of the individual is responsible of the emergence of lesions, after a minimal exposure to sunlight.

In medical terms is known as “solar urticaria” a rare allergy which affects to less than two percent of individuals exposed to sunlight. This allergy to sunlight is not inherited, and there is no collective group with bigger tendency to develop this condition.

Symptoms of solar urticaria

The urticaria is an allergic reaction which affects mostly to people who have been affected by other allergies like the angioedema, hay fever, immunological factors, infectious factors, medicinal factors and nutritional factors. On fifty percent of the cases a clear triggering for this condition cannot be found. On kids population the urticaria is more frequently associated to breathing infections or to the foods that are ingested.

In these cases solar urticaria is manifested as the emergence of hives that appear on the skin surface accompanied by itching. The release of histamine and other chemical substances on blood stream (in part an allergic response) causes pruritus, localized inflammation and other symptoms.

Diagnosis of solar urticaria

The diagnosis is mainly based on the aspect of the skin and it is confirmed with the help of a photo test. This test consists on reproducing the lesions a few minutes after the exposition to a natural source of light such as sunlight or to an artificial source of light like a quartz lamp or a fluorescent tube. The use of filters can separate the reactivity on its different types. It is useful for the confirmation of the diagnosis to consider a background of reactions to antigens. In occasions there can also be used blood tests.

The abnormal delayed response can help to difference patients affected by polymorphous solar flare. Cutaneous symptoms of the erythropoietic protoporphyria always begin before the patient reaches the age of thirteen years, and patients and their families present an increment of protoporphyrin in erythrocytes and sometimes in feces.

The differential diagnosis must be done with the photo sensibility induced by medicines and with the solar polymorphic eruption. The last one is a recurrent dermatitis of an unknown origin which is present on areas of the skin which are exposed to light during seasons of heat disappearing then in winter. A few hours after the exposition to sunlight start to emerge erythematous and pruritic papules which can confluence forming plaques and which unlike the case of solar urticaria can persist during the following days. With less frequency there can be observed the emergence of eczematous plaques with vesiculation. It should be differenced too the process that have incidence on the worsening of lesions in the presence of sun.