Figure 1: The structure of the skin. The skin is composed of the epidermis, dermis, and subcutaneous fat tissue. The pilosebaceous-apocrine units are a combination of the hair follicle, sebaceous gland, and apocrine gland. The hair follicles are always associated with sebaceous glands. However, apocrine glands have limited distribution and are mainly located in the axillary area. In the hair follicle, the outer root sheath is an epithelial extension of the interfollicular epidermis. The inner root sheath is located between the outer root sheath and the hair shaft. There is an independent skin appendage, the eccrine gland, which can secrete sweat. The figure was drawn by using the commercial web-based software purchased from BioRender.com.