L56: Other acute skin changes due to ultraviolet radiation

L56.4: Polymorphous light eruption

The condition referred to as “sun allergy” is actually not an allergy. It is not yet known for sure what causes the skin lesions in this condition. After the skin has been exposed to sunlight, the skin lesions form within a few hours or days. The skin can become red or swell up in the affected areas. Small papules or blisters may form, too. The affected areas of the skin can be very itchy.

Areas of the skin that are exposed to the sun without protection are particularly affected. The skin lesions occur mainly in spring or early summer on skin that is still untanned. When the skin gets used to the sun as the summer wears on, these kinds of skin lesions are rarer.