eMedicine Specialties > Dermatology > Allergy & Immunology

Urticaria, Solar

Author: Elma D Baron, MD, Assistant Professor of Dermatology, Case Western Reserve University, University Hospitals of Cleveland; Director of Skin Study Center, University Hospitals Research Institute; Acting Chief of Dermatology, Veterans Affairs Medical Center, Cleveland
Coauthor(s): Charles R Taylor, MD, Assistant Professor of Dermatology, Harvard Medical School; Director of Phototherapy Unit, Department of Dermatology, Massachusetts General Hospital
Contributor Information and Disclosures

Updated: Mar 29, 2007

Introduction

Background

Solar urticaria is a rare photodermatosis characterized by pruritus, stinging, erythema, and wheal formation after a brief period of exposure to natural sunlight or an artificial light source emitting the appropriate wavelength.

Initially described by Merklen in 1904, the reaction is localized to exposed areas of the skin, although it can occur through thin clothing. Solar urticaria disappears within several minutes to a few hours, without pigmentary change if further sun exposure is avoided. This disorder can be quite disabling and difficult to manage. It often has a sudden, dramatic onset, and little information is available regarding its duration and eventual outcome.

Pathophysiology

Solar urticaria is possibly caused by an antigen-antibody reaction. Solar irradiation may induce an antigen in the serum or plasma of affected individuals. Intradermal injection of serum from a solar urticaria patient passively, but not consistently, transfers the condition to a healthy individual.

The following types of solar urticaria have been proposed:

• Type I: This type is an immunoglobulin E (IgE)–mediated hypersensitivity to specific photoallergens generated only in solar urticaria patients.
• Type II: This type is an IgE-mediated hypersensitivity to nonspecific photoallergens found in both solar urticaria patients and healthy individuals.

Passive transfer test findings are positive in patients with type II solar urticaria, but they may be positive or negative in those with type I.

The wide action spectrum (290-800 nm) implicated for this condition may be related to the specific photoallergen and its molecular weight. Diversity in the reported action spectra may be due to differences in photoallergens. In addition, spectra believed to be responsible for either inhibition or augmentation of the reaction have been detected. Complex interactions occur between the various wavelengths and the photoallergen.

The result of these interactions is mast cell degranulation with subsequent histamine release. Mediators other than histamines may also be involved. Inhibition of solar urticaria with light suppresses the wheal-flare response following intradermal injection of photoactivated autologous serum but does not suppress the wheal and flare associated with compound 48/80.

Frequency

United States

Solar urticaria comprises only 4% of US patients with photosensitive disorders.

International

Solar urticaria comprises 5.3% of the cases of photosensitive dermatoses worldwide.

Mortality/Morbidity

The mortality rate has not been determined. In some cases, skin eruption is accompanied by symptoms such as headache, nausea, vomiting, bronchospasm, and syncope.

Race

The condition occurs in all races.

Sex

A slight female predilection is noted.

Age

Solar urticaria has a wide range of onset (10-70 y). The mean age of onset is 35 years, but it has been reported to occur in infancy.

Clinical

History

An accurate history is important for the diagnosis of solar urticaria because of the transient nature of the eruption. Patients often have no obvious lesions.

• Patients may report pruritus, erythema, and wheal formation of varying degrees after a short period (<30 min) of sun exposure.
  • As with most other photodermatoses, skin lesions in solar urticaria may occur on any exposed area, even if skin was covered with thin clothing.
  • The face and the dorsal aspect of the hands, which are chronically exposed to the sun, are less severely affected than other parts of the body, perhaps owing to acclimatization and "hardening."
• Mucosal involvement (eg, tongue and/or lip swelling) has been reported.
• Other symptoms, such as headache, nausea, vomiting, bronchospasm, and syncope, have been reported but are considered rare.
• Upon cessation of sun exposure, the rash begins to disappear within several minutes to a few hours and rarely lasts beyond 24 hours. Rapid disappearance of the rash upon cessation of further sun exposure is essential to the diagnosis of solar urticaria.
• Ascertain the following aspects of history to exclude other differential diagnoses:
  • Oral medication intake (eg, chlorpromazine), which may cause a similar photo-induced reaction
  • Currently used topical agents (eg, sunscreen, fragrance), which can cause photocontact dermatitis
  • Family history of photosensitivity (as may occur in some porphyrias)
  • Medical history regarding other body systems in order to detect other underlying causes of photosensitivity (eg, connective-tissue disorders)

Physical

In most cases, physical examination findings will be normal.

• During an acute episode, vital signs are usually unaffected; however, systemic symptoms accompanying the cutaneous eruption have been reported.
  • In rare cases, cardiac and respiratory rates increase and blood pressure decreases.
  • Wheezing may be heard upon auscultation of the chest when bronchospasm is present.
• Examination of the skin during an acute episode may reveal lesions in the form of erythematous macules to distinct wheals, the morphology of which may be no different from that of lesions found in acute urticaria secondary to other causes.
  • Eruption follows a photodistribution modified by the type of clothing worn by the affected individual at the time of exposure.
  • Lesions may be present in areas covered with thin clothing, depending on the causative light wavelength and sheerness of the fabric.
  • Mucosal areas, such as the tongue and lips, may be swollen or edematous.
  • The reaction leaves no residual skin changes. Consequently, examination of the skin after the acute eruption reveals no evidence of the condition.

Causes

Solar urticaria may be caused by an antigen-antibody reaction. Solar irradiation may induce an antigen in the serum or plasma of affected individuals. Intradermal injection of serum from a solar urticaria patient passively, but not consistently, transfers the condition to a healthy individual.

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