The skin is the largest organ of the human body, wrapping our whole body, and the closest contact with the outside world, so the skin human body’s first line of defense against external harmful substances, subcutaneous tissues and internal organs are protected by her to a greater or lesser extent. Some internal organs and other systemic diseases can also be reflected to the skin. If a person is physically fit, his or her skin is often normal, and the skin appears soft and lustrous, elastic and evenly colored. The color of the skin varies greatly depending on race, age, gender, and location. The skin is composed of epidermis, dermis, subcutaneous tissue, skin appendages, blood vessels, lymphatic vessels, muscles, and nerves, and can have a complex structure. The thin skin has protective effects against mechanical irritation, physical damage, chemical damage, and microbial attack, as well as sensory effects, temperature regulation, secretion and excretion, absorption of certain substances such as drugs and water, important metabolic effects, and immune effects. When suffering from certain systemic diseases, some abnormal changes may occur in the skin or the hair, etc. Many allergic reactions to drugs and food are also first manifested on the skin, and endocrine disorders can also cause changes in skin color and shape. These changes remind us of the need to make early diagnosis of certain diseases, where the skin really plays the role of a “health indicator”.