Allergic reaction to the sun is considered a lymphocyte-mediated delayed allergic reaction, which belongs to the category of immune reactions, but must be attended by light energy, and occurs in a small group of people with allergic qualities. When allergic substances are present in the skin, after stimulation by irradiation and after a period of latent work again, eczema-like manifestations such as small papules, blisters, erythema, vesicles, exudation, etc. appear from exposed areas, which can induce or stimulate UV light working at long-wave or medium-wave wavelengths. Then the photosensitive material absorbs the light energy and undergoes corresponding chemical changes, resulting in semi-antigens combining with skin tissue proteins to form complete antigens to stimulate the body and produce corresponding antibody interactions leading to allergic reactions.