Shedding Light on Photosensitivity Disorders
We can develop allergies to many things in our environment – our pets, the trees in our backyard or even certain medications, like penicillin. When thinking about allergies, common ones such as asthma and food allergies often come to mind; however, there are a large number of allergies that are both rarer and more life threatening. Imagine, all of a sudden, being unable to go outside without feeling a burning sensation all over your skin. Imagine having to hide your skin under layers of clothes just to carry out your day.
Approximately 1 in 10,000 individuals have an allergy to light, a condition termed solar urticaria.1 Within just minutes of exposure, individuals with this rare photosensitivity disorder develop a rash. The symptoms of solar urticaria are much different from sunburn. Individuals develop red skin welts that itch or burn after exposure to ultraviolet or visible light. These symptoms can appear after exposure either to the sun or artificial lighting.1,2 Aside from the rash, patients suffering from solar urticaria can also experience headaches, dizziness, wheezing, nausea, and systemic collapse.3 This disease is chronic in nature, and its effects can last for over a decade.4 Although solar urticaria is rare and the exact etiology of the disease is not fully understood, it should not be taken any less serious than other more common allergies.
When our bodies have an allergic reaction, there are a series of events happening on a molecular and cellular level. Our body mistakenly detects an innocuous substance in our environment as something harmful. Substances that cause an allergic reaction, such as certain foods or plant pollen, are called allergens. After exposure to an allergen, our immune system produces antibodies (namely IgE) specific to that allergen. Antibodies usually help the immune system recognize and clear harmful foreign pathogens, but in the case of allergies, they are produced against something that is not actually harmful to the body. IgE antibodies trigger specific immune cells, called mast cells, to release inflammatory chemicals into the bloodstream. Histamine is one of these chemicals, and it is mainly responsible for the symptoms of allergic reactions, such as itchy eyes, runny nose, sneezing, skin rashes, and nausea.
In solar urticaria, light energy is absorbed by the skin and a “photoallergen” is produced, the exact identity of which is unknown.4 This photoallergen is then recognized by specific IgE antibodies, which then bind to mast cells. Upon binding, the mast cells degranulate, releasing histamine and other inflammatory chemicals. This entire process is thought to lead to the red, itchy skin welts experienced by individuals with solar urticaria.
Management of the often severe symptoms associated with solar urticaria can be quite difficult. Sun protection with layers of clothing and a broad spectrum sunscreen is important, but it is often not enough. Oral antihistamines are an available treatment; however, they are not effective for all patients, especially in severe cases.5 As a result, most individuals turn to phototherapy for temporary relief of their symptoms. Through repeated exposure to UV radiation or visible light, phototherapy causes patients to become desensitized to light.6 This type of treatment works on a similar principle to desensitizing children with peanut allergies by feeding them small and increasing amounts of peanuts daily. Although effective, phototherapy puts patients at an increased risk of developing skin cancer, as well as anaphylaxis.7
Solar urticaria can be severely debilitating and can largely affect an individual’s day-to-day life. A study looking at the quality of life in children with solar urticaria and other photosensitivity disorders found that the greatest impact is on outdoor activities, followed by holiday plans and school activities. Itching and needing to wear special clothes are also important concerns for these children.8 The New Yorker recently published an article entitled A Decade Lived in the Dark, depicting the life of Anna Lyndsey, a British woman living with an extreme light sensitivity.9 Several years ago, Anna Lyndsey developed a burning sensation all over her body that she has linked to light exposure. Her pain has forced her to quit her desk job, and she now spends many of the daylight hours in a dark room that she created in her home. Being unable to tolerate sunlight makes it difficult for her to visit doctor’s offices and to receive medical treatment. The specialists and dermatologists she has seen have been unable to successfully treat her symptoms.
The future, however, is bright for patients with solar urticaria. There have been recent advances in potential treatment for this disease.3,5,10 Omalizumab is a drug currently in clinical trials that tries to selectively bind to IgE antibodies, thus inhibiting the binding of IgE to mast cells. This stops the mast cells from degranulating and causing solar urticaria, as the antibody cannot bind to the mast cells and trigger an allergic reaction.5 Although this treatment has been shown to be effective, it still does not provide complete relief of itching and other symptoms. There also needs to be more investigation into defining the ideal dose, dose schedule and duration of treatment.10
1. Orphanet: Solar urticaria. 2008; http://www.orpha.net/consor/cgi-bin/index.php.
2. Saini S. Chronic Spontaneous Urticaria - Etiology and Pathogenesis. Immunology and Allergy Clinics of North America. 2014(34):33-52.
3. Adamski H, Bedane C, Bonnevalle A, et al. Solar urticaria treated with intravenous immunoglobulins. J Am Acad Dermatol. 2011;65(2):336-340.
4. Beattie PE, Dawe RS, Ibbotson SH, Ferguson J. Characteristics and prognosis of idiopathic solar urticaria: a cohort of 87 cases. Arch Dermatol. 2003;139(9):1149-1154.
5. Güzelbey O AE, Magerl M, Zuberbier T, Maurer M, Metz M. Successful treatment of solar urticaria with anti-immunoglobulin E therapy. Allergy. 2008 (63):1563-1565.
6. Lugovic Mihic L, Bulat V, Situm M, Cavka V, Krolo I. Allergic hypersensitivity skin reactions following sun exposure. Coll Antropol. 2008;32 Suppl 2:153-157.
7. Solar urticaria (SU). 2014; http://www.clinuvel.com/en/skin-science/skin-conditions/rare-skin-conditions/solar-urticaria-su.
8. Rizwan M, Haylett AK, Richards HL, Ling TC, Rhodes LE. Impact of photosensitivity disorders on the life quality of children. Photodermatol Photoimmunol Photomed. 2012;28(6):290-292.
9. Cesar E. A Decade Lived in the Dark. New Yorker. September 26, 2016.
10. Sussman G, Hebert J, Gulliver W, et al. Insights and advances in chronic urticaria: a Canadian perspective. Allergy Asthma Clin Immunol. 2015;11(1):7.
Cite This Article:
Peacock E., Zheng K., Chan G., Ho J. Shedding Light on Photosensitivity Disorders. Illustrated by P. Taarea. Rare Disease Review. January 2017. DOI:10.13140/RG.2.2.10307.60964.