Allergic reactions to sunlight occur when ultraviolet radiation triggers changes in your skin cells. These changes cause your immune system to mistake proteins in your skin for harmful substances, causing allergy symptoms. Most people with sun allergies suffer symptoms only when exposed to bright sunlight during spring and summer months; however, people with severe sun allergies can have reactions even during winter months.
An allergic reaction to UV rays can cause a variety of symptoms, including rashes, swollen skin, hives, blisters and itchy skin. It isn't clear why some people have a sun allergy, but doctors think genetics may play a role. Sun allergies can be treated using oral antihistamines, topical steroid creams and UV therapy, but the best way to prevent a reaction is to avoid exposure to the sun.
Certain medications, medical conditions or chemicals in hair or skin products can cause increased photosensitivity, but this isn't a true allergic reaction to the sun.