Solar Urticaria (SU) is an allergic or immune reaction to the sun, UV and visible light. Although rare, it can arise in any person, at any time and diagnosis is difficult due to its superficial similarity to other allergies and conditions. For example, it is often mistaken for Polymorphous light eruption (PMLE), lupus erythematosus and even erythropoietic protoporphyria (EPP).
SU causes an itchy, burning redness of the skin after exposure to sunlight. Longer or more extreme exposure can result in ‘wheals’ or hives and alongside cutaneous symptoms, patients can often experience headaches, nausea, light-headedness and fainting or even difficulty breathing.
As this condition is an allergic reaction, the effects can be felt within five minutes of being exposed to the sun and usually disappear within 24 hours, sometimes as quickly as half an hour.
Common allergies are a reaction to an introduced substance in the body or on the skin, be it a drug, food or airborne particle, to which the immune system reacts with an extreme inflammatory response. SU causes the same kind of response but the allergen, known as a photoallergen, is created by their own bodies upon exposure to sunlight.
Existing treatments experience varying degrees of effectiveness. Some success has been had administering strong antihistamines prior to exposure to sunlight. There have also been attempts at desensitisation and immunosuppression, however both of these carry their own risks. Desensitisation can trigger severe reactions and must be committed to long term to maintain its effectiveness, this introduces a heightened risk of skin cancer. In extreme cases plasmapheresis can be considered. This process involves removing blood plasma or fluid from red blood cells and then returning these cells to the body.
A common way for sufferers to control their condition is to change their behaviour and lifestyle so that they avoid exposure to the sun. This is obviously inhibitive and difficult, but so far the best way to prevent severe reactions.
In July this year we announced positive results from our phase II study.