Solar urticaria is a rare, IgE-mediated, 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. (See Presentation.)
Initially described by Merklen in 1904, solar urticaria 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. The condition 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. (See Prognosis, Presentation, DDx, Treatment, and Medication.)
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Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria.jpg).
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Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria1.jpg).
Solar urticaria accounts for only 4% of patients in the United States with photosensitive disorders and for 5.3% of cases of photosensitive dermatoses worldwide.
The disorder has been reported in all skin types and ethnic groups, worldwide, with a slight female predilection. Regarding age, the disease has a wide range of onset (10-70 y). Typical onset is 20-40 years.[1] The mean age of onset for solar urticaria is 35 years, but it has been reported to occur in infancy.[2, 3]
Educate patients that, despite its persistent and chronic nature, solar urticaria is a benign disorder that is 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. (See Prognosis, Treatment, and Medication.)
For patient education information, see the Allergies Center and the Skin Conditions and Beauty Center, as well as Hives and Angioedema.
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 characterized by an immunoglobulin E (IgE)–mediated hypersensitivity to specific photoallergens generated only in solar urticaria patients
Type II - This type is characterized by an IgE-mediated hypersensitivity to nonspecific photoallergens found in solar urticaria patients and in 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 solar urticaria may be related to the specific photoallergen and its molecular weight. Diversity in the reported action spectra for the disease 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.[4]
Complex interactions occur between the various wavelengths and the photoallergen.[5]
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.[6]
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.
In some cases, skin eruption is accompanied by symptoms such as headache, nausea, vomiting, bronchospasm, and syncope. The mortality rate for solar urticaria has not been determined.
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. Headache, nausea, vomiting, bronchospasm, and syncope have been reported as well 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 the patient’s 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, such as connective-tissue disorders
In most cases of solar urticaria, physical examination findings will be normal. During an acute episode of solar urticaria, 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 solar urticaria episode may reveal lesions in the form of erythematous macules to distinct wheals. Although the lesions’ morphology may be no different than that of lesions found in acute urticaria secondary to other causes, the eruption will follow a photodistribution modified by the type of clothing worn by the affected individual at the time of exposure.
Lesions may also 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 an acute eruption reveals no evidence of the condition.
There are no specific laboratory tests for diagnosis. In order to rule out other conditions, perform serologic tests for antinuclear antibody, Ro, and La antibodies to exclude connective-tissue disease (eg, lupus erythematosus).
Perform testing to exclude metabolic causes (eg, porphyrias). Evaluate the plasma porphyrin level; if abnormal results are found, follow with a quantitative 24-hour urinary and fecal porphyrin measurement, as well as erythrocyte porphyrin determination.
Histologic findings
Histologic changes are typically found in the dermis in the form of vasodilatation, increased permeability of the vascular endothelium, and edema. Eosinophil infiltration and deposition of eosinophil granule proteins in the dermis are prominent during the early stages of the lesion. Neutrophils are found in increased numbers around the upper dermal vessels. Dermal mast cells may increase in number. After 24 hours, the dermal infiltrate is predominantly composed of mononuclear leukocytes.
Phototesting confirms the diagnosis, identifies the action spectrum, and establishes baseline data (eg, minimum urticarial dose [MUD]) for possible therapeutic interventions and monitoring in the future.
Solar urticaria has a wide action spectrum. Perform phototesting using broadband ultraviolet B (UV-B; 290-320 nm), UV-A (320-400 nm), and visible light sources (400-800 nm). Most patients with solar urticaria have provocative wavelengths in the UV-A and visible ranges, especially green or blue.
Duration of exposure under visible light should be less than an hour. Typically, the light emitted by a slide projector is used. Measures must be taken to avoid excessive heat output from the light source in order to eliminate the possibility of cholinergic or heat-induced urticaria, instead of actual solar urticaria. A water filter may be placed in front of the light source to absorb excess heat.
Phototesting with narrowband UV-B (311-313 nm) is recommended if therapy with this light source is being considered. Occasionally, these tests do not produce the expected reaction.
Phototesting with other light sources (eg, solar simulators, lasers) may be necessary in difficult-to-establish cases. Provocation with natural sunlight may be performed if ambient conditions allow.
Many patients with solar urticaria have an inhibition spectrum. If their skin is first exposed to wavelengths known to induce solar urticaria and is then immediately afterward, or possibly concurrently, exposed to radiation within the inhibition spectrum, the urticarial reaction is either eliminated or diminished.
Treatment of solar urticaria can be frustrating. A combination of different modalities is often necessary, but the success of these methods is highly variable. Taking measures to avoid or minimize sun exposure is the most important step for patients with solar urticaria. Unfortunately, this often requires major adjustments in lifestyle, which might be impractical for some patients.
Long-acting, nonsedating H1-receptor blockers are the first line of treatment for solar urticaria. This is because the disease involves IgE-mediated mast cell degranulation with consequent histamine release.
Phototherapy with UV-A,[9] broadband UV-B, or narrowband UV-B or photochemotherapy with oral methoxsalen (8-MOP, a form of psoralen) plus UV-A is also effective for treating solar urticaria.
In rare systemic cases of the disease, supportive medical measures to maintain blood pressure and adequate ventilation may be required if extensive cutaneous surfaces are simultaneously involved.
One case report described two cases of idiopathic solar urticaria treated with intravenous (IV) immunoglobulin, with durable remissions of 13 months and 4 years. Treatment was with 2 g/kg over several 5-day courses approximately 1 month apart.[10] Another case report also described successful treatment of solar urticaria with IV immunoglobulin and suggested that it be discussed as a therapeutic option if high-dose antihistamines provide unsatisfactory results.[11, 12]
Omalizumab, an anti-IgE antibody approved for use for chronic spontaneous urticaria, has been reported to be effective in the treatment of solar urticaria.[13, 14, 18] Use of the medication for solar urticaria is currently off-label. A small, single-arm, French study administered 300-mg subcutaneous doses of omalizumab every 4 weeks for three total visits; despite some improvement, results were lackluster.[15]
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.[16] However, therapy has been reported to be ineffective in some centers. Until definitive studies are conducted to evaluate the efficacy of this therapy, it should be reserved as a last resort.
The success of antihistamine therapy depends on disease severity. For example, antihistamine monotherapy would probably not benefit someone who develops hives after just a few seconds of sun exposure, but it would help a patient who requires at least 10 minutes’ sun exposure before hives appear.
Antihistamines seem to block wheal response and minimize pruritus, but they do not entirely eliminate an erythematous reaction. This should be explained to the patient.
As previously mentioned, phototherapy with UV-A,[9] broadband UV-B, or narrowband UV-B or photochemotherapy with the psoralen agent oral methoxsalen (8-MOP) plus UV-A is 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.[17]
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.
A number of treatment protocols are used for the different light sources mentioned, but the optimal protocol has not been clearly established.
Minimum urticarial dose
The minimum urticarial dose (MUD) with the specific light box being used in the treatment of solar urticaria 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 using UV-A alone may be performed until the MUD is increased to a level at which oral methoxsalen photochemotherapy can be initiated.
Mechanisms of action
The mechanisms of action for phototherapy and photochemotherapy in solar urticaria are not entirely known. The resulting epidermal thickening and increase in skin pigmentation 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.
Sun exposure must be avoided or minimized because it is the primary causative agent of solar urticaria. Educate patients about practical measures, such the following:
Wearing protective clothing
Judiciously applying sunscreens with adequate protection against the causative wavelengths
Using UV protective shields over glass windows
Altering lifestyle to minimize time spent outside during the day - Ie, changing job hours and shifting to indoor recreational activities
Some patients with UV-A or visible, induced solar urticaria may find it helpful to use 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.
Because solar urticaria involves IgE-mediated mast cell degranulation with consequent histamine release, the first line of treatment for this disease consists of long-acting, nonsedating H1-receptor blockers. Often, such agents achieve a protective factor of 10 or more. The H2-receptor antagonist ranitidine and others may aid in treatment when an H1 blocker is not effective on its own.
Antimalarial agents can treat certain photosensitive eruptions, including those of solar urticaria, but their efficacy is unpredictable.
Patients with solar urticaria that is resistant to treatment with antihistamines have experienced promising results with injections of omalizumab.[13, 14, 18]
Clinical Context:
Cetirizine forms a complex with histamine for H1-receptor sites in the blood vessels, gastrointestinal (GI) tract, and respiratory tract.
Clinical Context:
Fexofenadine competes with histamine for H1 receptors in the GI tract, blood vessels, and respiratory tract, reducing hypersensitivity reactions. The drug does not sedate.
Clinical Context:
Desloratadine is a long-acting tricyclic histamine antagonist selective for H1 receptors. It relieves nasal congestion and systemic effects of seasonal allergy. The drug is a major metabolite of loratadine, which, after ingestion, is metabolized extensively to active metabolite 3-hydroxydesloratadine.
The extent to which antihistamines are useful against solar urticaria depends on the severity of the disease itself. For example, someone who gets hives after just a few seconds of sun exposure is unlikely to benefit from antihistamine monotherapy, while a patient requiring 10 minutes or more of exposure would show more benefit. Antihistamines seem to block wheal response and minimize pruritus, but they do not entirely eliminate an erythematous reaction. This should be explained to the patient.
Clinical Context:
Hydroxychloroquine inhibits chemotaxis of eosinophils and the locomotion of neutrophils. It impairs complement-dependent antigen-antibody reactions. Hydroxychloroquine sulfate 200 mg is equivalent to 155 mg hydroxychloroquine base and 250 mg chloroquine phosphate.
Clinical Context:
Ranitidine is an H2 antagonist that, when combined with the H1 type, may be useful in treating allergic reactions that do not respond to H1 antagonists alone.
Clinical Context:
This agent competitively inhibits histamine at the H2 receptor of the gastric parietal cells, resulting in reduced gastric acid secretion, gastric volume, and reduced hydrogen concentrations.
Clinical Context:
This agent inhibits histamine at H2 receptors of gastric parietal cells, which results in reduced gastric acid secretion, gastric volume, and hydrogen concentrations.
Marc Zachary Handler, MD, Fellow in Mohs Micrographic Surgery, Skin Laser and Surgery Specialists of NY and NJ
Disclosure: Nothing to disclose.
Chief Editor
Dirk M Elston, MD, Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine
Disclosure: Nothing to disclose.
Additional Contributors
Ani L Tajirian, MD, Procedural Fellow, Division of Dermatology, University of Vermont College of Medicine
Disclosure: Nothing to disclose.
Philip J Cohen, MD, Chief, Section of Dermatology, New Jersey Veterans Affairs Medical Center
Disclosure: Nothing to disclose.
Acknowledgements
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
Elma Baron, MD is a member of the following medical societies: American Academy of Dermatology, American Society for Photobiology, Photomedicine Society, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.
Donald Belsito, MD Professor of Clinical Dermatology, Department of Dermatology, Columbia University Medical Center
Donald Belsito, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Contact Dermatitis Society, Dermatology Foundation, New York County Medical Society, New York Dermatological Society, Noah Worcester Dermatological Society, and Phi Beta Kappa
Disclosure: Nothing to disclose.
Jeffrey Meffert, MD Assistant Clinical Professor of Dermatology, University of Texas School of Medicine at San Antonio
Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, and Texas Dermatological Society
Disclosure: Nothing to disclose.
Charles R Taylor, MD Associate Professor of Dermatology, Harvard Medical School; Director of Phototherapy Unit, Department of Dermatology, Massachusetts General Hospital
Charles Taylor, MD is a member of the following medical societies: American Academy of Dermatology, American Society for Laser Medicine and Surgery, Massachusetts Medical Society, New England Dermatological Society, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.
Michael J Wells, MD Associate Professor, Department of Dermatology, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine
Michael J Wells, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, and Texas Medical Association
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