Last updated: 25 September 2008.
Introduction
SU is a rare and severe disorder following exposure to sun and or light, occurring in less than 1% of the population.
Incidence
Solar UrticariaSolar Urticaria is a rare and severe allergic disorder following exposure to sun and or light, occurring in less than 1% of the population. Click here for more. is rare. 3.1 per 100,000 people are affected and females are more likely to be affected than males. Solar UrticariaSolar Urticaria is a rare and severe allergic disorder following exposure to sun and or light, occurring in less than 1% of the population. Click here for more. occurs world wide.
Symptoms
Following limited exposure to sunlight, sufferers may develop an itchy or burning redness on exposed skin. More prolonged exposure can result in the rapid development of characteristic "wheals" or round red raised areas on the skin. These symptoms can also be accompanied by headache, nausea, breathing difficulty or fainting. The symptoms usually develop soon after sun exposure and last anywhere from 30 minutes to 24 hours.
Causes
Solar UrticariaSolar Urticaria is a rare and severe allergic disorder following exposure to sun and or light, occurring in less than 1% of the population. Click here for more. may be primary or secondary.
Primary solar urticaria is an immediate hypersensitivity (allergic) reaction towards an allergen induced in the body following sunlight exposure. The responsible allergen is not know but is termed a photoallergen. The allergic reaction that follows prolonged sunlight exposure leads to a widespread inflammatory response.
UVA and visible light are the wavelengths known to trigger the reaction.
Secondary Solar UrticariaSolar Urticaria is a rare and severe allergic disorder following exposure to sun and or light, occurring in less than 1% of the population. Click here for more. occurs in association with other photosensitivity disorders such as cutaneous porphyria or lupus or with certain medications known to cause photosensitivity.
Treatment
Treatment is usually directed towards relief of symptoms. Most commonly, antihistamines with or without systemic steroids are used. Desensitization with UV light sources has been used but this carries the risk of provoking symptoms. Immunosuppressants such as cyclosporin and intravenous immunoglobulins have also been used.
In extreme cases these patients need to be hospitalized to undergo plasmaphoresis (a procedure similar to dialysis where the plasma in their blood is removed and the blood cells are returned to the patient).
Prognosis
Most patients experience symptoms of Solar UrticariaSolar Urticaria is a rare and severe allergic disorder following exposure to sun and or light, occurring in less than 1% of the population. Click here for more. throughout their lifetime. Rarely, symptoms may worsen but one quarter of patients will have complete resolution after 10 years.
Introduction
SU is a rare, sunlight induced hypersensitivity (allergic) reaction that causes wheals (raised red skin welts) very soon after or during sun or light exposure. In Solar Urticaria, the reaction is triggered by exposure to UV or visible light. It may be severely disabling and can even be life threatening.
Epidemiology and prevalence
An estimated 3.1 per 100,000 people are affected by SU and it is believed to occur world wide. There is a higher preponderance in females than males.
Clinical Features
Solar Urticaria may arise at any age, with the episode occurring after marked sunlight exposure. Initial presentation has also been reported after first solarium use. Symptoms usually develop within 5 minutes of sun exposure and often develop from an unpleasant sensation to itching, redness and swelling, followed by localized or widespread development of wheals (an urticarial flare). Gradual resolution then follows over 1-2 hours.
Rarely, a more prolonged exposure may be required for symptoms to develop, or the onset of symptoms may be delayed for several hours. With extensive whealing some patients also experience headache, nausea, bronchospasm (asthma-type respiratory symptoms) and syncope (dizziness) which may become life threatening (although this is rare). Conversely, in some people with mild disease, or in those who quickly recognize their onset and avoid further exposure, whealing may not be reported.
Sun-exposed areas are most commonly affected, although occasionally reactions are seen in dermal areas that are not exposed to the sun. Rarely sun-exposed sites are spared suggesting that tolerance may occur.
Etiology and pathogenesis
Primary Solar Urticaria is an immediate Type 1 hypersensitivity response (IgE mediated allergic reaction) towards a photo-allergen which is a compound produced in the body when UV light is absorbed by a cellular pre-cursor. Mast cell degranulation and histamine release are important factors in SU but many other inflammatory cells, particularly neutrophils and eosinophils are involved in amplifying the whealing response.
Many wavelengths light may trigger the production of different photo-allergens but SU is most commonly caused by UVA or visible light. There appears to be no genetic basis for this condition. Very rarely secondary SU occurs in association with drug photosensitivity, cutaneous porphyria or lupus.
Diagnosis
Photo testing confirms the diagnosis and reveals the wavelengths responsible for inducing an urticarial response. Photo testing may be performed with a monochromator (single wavelengths of light selected at a time), broad spectrum source or natural sunlight to estimate the minimal dose of sunlight required to induce symptoms. Screening tests to exclude lupus (ANA,eNA) and cutaneous porphyria (porphyrin studies) must be done to exclude these conditions. Medications must also be considered as a possible cause.
Differential diagnosis
Conditions that may cause secondary Solar Urticaria
Treatment
The mainstay of treatment is behavioural change, avoidance of sunlight, photo protective clothing and broad-spectrum sunscreens, however this may not always be useful in cases of visible light being responsible for the Solar Urticaria. High doses of H1-antihistamines taken an hour before sun exposure are very effective in one third of patients and give another third partial relief. Desensitization with phototherapy may be useful for some patients however therapy generally needs to be continued to maintain its benefit and so consequently carries a risk of long-term risks such as skin cancers. In severely affected individuals, this treatment also carries the risk of anaphylaxis (severe, often life threatening allergic reaction) and so should be undertaken with extreme caution. Immunosuppressant medications such as Cyclosporin or plasmapheresis may need to be considered in the most severe cases.
Prognosis
For the majority of patients symptoms will persist indefinitely. For a small proportion of patients Solar Urticaria will deteriorate however some do experience improvement with an estimated 26% chance of resolution at 10 years.
References
- Dice, J P. (2004). 'Physical Urticaria', Immunology and Allergy Clinics of North America, 24, pp225-246.
- Roelandts, R (2003). 'Diagnosis and treatment of solar urticaria" Dermatologic Therapy, pp52-56.
- Beattie, P E, Dawe, R S, Ibbotson, S H, & Ferguson, J. (2003) 'Characteristics and prognosis of idiopathic solar urticaria: A cohort of 87 cases', Archives of Dermatology. 139 (9), pp1149-1154.
- Buxton, P K, (2003). ABC of Dermatology. London: BMJ Publishing Group Ltd.
- Ng, J H C, Foley, P A, Crouch, R B, & Baker, C S. (2002). 'Changes of Photosensitivity and Action Spectrum with Time in Solar Urticaria', Photodermatology, Photoimmunology & Photomedicine, 18, pp191-195.
More References on Solar Urticaria
Clinuvel Photoprotection Reference Library
Associations and online resources
Access to:
International Chronic Urticaria Society
Sun1 patient support group information on SU
