[Medical Q&A] Can sun exposure also make your skin sick?

Author: Zhou Yi, Associate Professor of Xi'an Medical College

Reviewer: Xiao Xinli, Associate Professor of Xi'an Jiaotong University

Solar dermatosis, which makes people think of skin problems in the hot summer, is actually a skin problem caused by prolonged or excessive exposure to sunlight. This type of skin disease not only affects the appearance, but may also cause considerable physical discomfort. Solar dermatosis can be divided into sunburn, phototoxic reaction and photosensitivity reaction according to different mechanisms of action.

The most common is sunburn. When you engage in outdoor activities for a long time without taking precautions against ultraviolet rays, a large amount of medium-wave ultraviolet rays will reach the basal layer of the epidermis of the skin and cause acute skin inflammation.

Phototoxic reaction is a non-immune reaction that will occur in any individual after being exposed to excessive sunlight. It can be divided into acute and chronic. Chronic phototoxic reaction is more common in people who suffer from long-term, repeated and heavy sunburn, such as seamen's skin, actinic keratosis, photoaging, etc.

Photosensitivity is a delayed hypersensitivity reaction mediated by lymphocytes, which is what we usually call allergy. Allergy to photosensitivity only occurs in a small number of individuals with photosensitivity. After absorbing light energy, photosensitizers undergo chemical changes to become haptens, and combine with macromolecules in the body to form complete antigens, stimulating the body to produce antibodies or cellular immunity and causing disease. According to the time of onset, it can be divided into immediate photosensitivity reactions (such as solar urticaria) and delayed photosensitivity reactions (such as polymorphic light eruption). Photosensitizers can be divided into endogenous (such as porphyrin) and exogenous (such as sulfonamide drugs, etc.).