Some of the most commented entries on this blog are those about sun allergies. I am under the impression that this condition is not widespread (at least not as common as food allergies), as there are not a lot of resources on the web discussing sun sensitivities and sun allergies. However, I can imagine how limiting and disabling it can be to suffer from this condition.

There are 4 common types of sun allergies or sun intolerance:

• Polymorphous light eruption (PMLE)
• Actinic prurigo
• Solar urticaria
• Photoallergic eruption

While they may share symptoms, only solar urticaria is considered to be a "true" form of an allergic to the sun reaction. In contrast to PMLE and actinic prurigo, solar urticaria shows hives or large itchy red patches on the sun-exposed skin usually within minutes of exposure. Photoallergic reaction, on the other hand, is a consequence of a reaction between sunlight and some chemicals applied onto the skin such as sunscreen, topical antibiotics, cosmetics and perfumes.

If you don't mind technical reading, here's an article on solar urticaria from eMedicine written by dermatologists Elma D Baron, MD and Charles R Taylor, MD.