eMedicine Specialties > Dermatology > Allergy & Immunology

Urticaria, Solar: Follow-up

Author: Ani L Tajirian, MD, Resident Physician, Department of Dermatology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School
Coauthor(s): Philip J Cohen, MD, Chief, Section of Dermatology, New Jersey Veterans Affairs Medical Center
Contributor Information and Disclosures

Updated: Nov 25, 2009

Follow-up

Further Outpatient Care

• Phototherapy with UV-A,⁷ broadband UV-B, or narrowband UV-B and photochemotherapy with oral methoxsalen (8-MOP) plus UV-A are effective for treating solar urticaria. Desensitization treatments are usually performed in the spring. Unfortunately, the tolerance induced by these modalities is often short-lived, and maintenance therapy is needed.
• A number of treatment protocols are used for the different light sources mentioned, but the optimal protocol is not clearly established.
• The minimum urticarial dose (MUD) with the specific light box to be used in the treatment must be determined.
  • The MUD is repeated during the course of treatment in order to monitor the patient's progress because development of tolerance is usually paralleled by an increase in the MUD.
  • If the initial MUD is very low, it is difficult to immediately start the patient on oral methoxsalen photochemotherapy. Initial exposures with UV-A alone may be performed until the MUD is increased to a level at which oral methoxsalen photochemotherapy can be initiated.
• Phototherapy and photochemotherapy mechanisms of action in solar urticaria are not entirely known.
  • The resulting increase in skin pigmentation and epidermal thickening may be important factors but are probably not the main mechanisms behind tolerance induction.
  • Some authorities have postulated a UV-induced increase in the mast cell degranulation threshold as a possible mechanism.
• Psoralen–UV-A, or PUVA, can cause disease improvement or remission lasting several months. Based on available evidence, it is probably the treatment of choice for patients not sufficiently helped by antihistamines.
• Plasma exchange therapy has been effective in a few cases, especially in patients with a circulating factor in their serum demonstrated by a positive intradermal test finding.⁸ However, therapy has been reported ineffective in some centers. Until definitive studies are conducted to evaluate the efficacy of this therapy, it should be reserved as a last resort.

Deterrence/Prevention

• Sun exposure must be avoided or minimized because it is the primary causative agent of solar urticaria. Educate patients about practical measures such as wearing protective clothing, judiciously applying sunscreens with adequate protection against the causative wavelengths, using UV protective shields over glass windows, and altering lifestyle to minimize time spent outside during the day (ie, changing job hours, shifting to indoor recreational activities). Some patients with UV-A or visible, induced solar urticaria may find helpful the use of self-tanning lotions containing dihydroxyacetone.
• If medical therapy is unsuccessful, some patients benefit from complete avoidance or, possibly, a combination of avoidance and medical therapy.

Prognosis

• Solar urticaria is usually a chronic condition. Few patients experience spontaneous remission. Continued intake of oral antihistamines may prevent the whealing to a degree, thus allowing some tolerance to sunlight. Significant and more long-lasting improvement is observed in patients who undergo phototherapy or photochemotherapy. Some patients find that following preventive measures makes their condition manageable.

Patient Education

• Educate patients that, despite its persistent and chronic nature, solar urticaria is a benign disorder usually localized to the skin without affecting general health. Emphasize that response to treatment is generally unpredictable and that prevention by avoidance may ultimately be the key to the management of this condition.
• For excellent patient education resources, visit eMedicine's Allergy Center and Skin, Hair, and Nails Center. Also, see eMedicine's patient education article Hives and Angioedema.

Miscellaneous

Medicolegal Pitfalls

• Ensure that an underlying condition that manifests as a photo-induced urticarial reaction (eg, lupus erythematosus, porphyrias) is excluded by conducting the necessary laboratory examinations.
• Patients must be well informed of the risks and benefits of antihistamines, phototherapy, photochemotherapy, or plasma exchange therapy if these modalities are considered.

The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors, Elma Baron, MD, and Charles Taylor, MD, to the development and writing of this article.

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