Possible pathological mechanism of “Radiation-irritated skin” and hyperpigmentation. Radiation may damage skin appendages, such as sweat gland, sebaceous gland, hair follicle and basement membrane. These damages may lead to the thickening of epidermis, atrophy of sweat gland and sebaceous gland, and hyperkeratosis. These may cause skin dryness and weakness of skin barrier. Radiation may also activate melanocytes, thereby promoting the formation of melanin and hyperpigmentation.