Solar urticaria is a rare, intermittent cutaneous eruption characterized by urticaria induced by ultraviolet and/or visible light. The inducible action spectrum varies by individual and may evolve with time but typically includes the ultraviolet A (UVA) and visible light spectrum; rarely, ultraviolet B (UVB) radiation may cause solar urticaria. While populations with lighter skin phototypes are more frequently affected, solar urticaria has also been reported to occur in African Americans.

Solar urticaria presents with classic urticarial wheals, erythema, and/or edema limited to sun-exposed areas of the body within minutes of sun exposure. Lesions typically resolve within 1-2 hours after exposure. Regularly sun-exposed areas, such as the face and dorsal hands, may be less sensitive due to the hardening phenomenon. Fixed solar urticaria is a subtype in which lesions occur exclusively in the same localized area of the skin.

Most patients experience accompanying pruritus or a burning sensation, and rarely pain has been described. Systemic symptoms are uncommon but may occur after prolonged exposure of a large body surface area to inciting radiation; symptoms may include headache, nausea, dizziness, wheezing, dyspnea, and syncope. Rarely, severe attacks are associated with anaphylactic shock.

Solar urticaria is caused by immunoglobulin E (IgE)-mediated mast cell degranulation. However, the exact mechanism triggering the degranulation is not known. It is thought to be an IgE-mediated response to a photoinduced allergen. Chlorpromazine, tar, benoxaprofen, and repirinast are known causes of drug-induced solar urticaria.

Solar urticaria typically follows a chronic course. The mean age of onset is 35 years, with less than 4% of patients presenting before age 5. Spontaneous resolution may occur in 15% of patients after 5 years and approximately 25% of patients after 10 years of symptoms. Occasionally, repeat exposure may produce a hardening effect with decreased severity or frequency of symptoms.