The skin, like other organs of the body, undergoes various morphological and functional changes as it ages. These changes can be divided into physiological aging, which is determined by genetic factors, and pathological aging, which is promoted by various environmental factors. Physiological aging is mainly characterized by wrinkles, pigmentation, sagging, and unexplained skin roughness. Aging of skin appendages is mainly common in gray hair, baldness, growth of ear and nose hair, and longitudinal nail crest. The most important factor of pathological aging is sunlight, especially ultraviolet light. It can both accelerate physiological aging and trigger pathological aging. The more common pathological aging are rhombic skin of the collar (i.e. mossy skin of the collar), senile pigmentation, senile leukoplakia, seborrheic keratosis (i.e. age spots), senile keratosis (solar keratosis) and malignant skin tumors, such as malignant nevus, basal cell carcinoma, malignant melanoma, etc. To delay physiological aging and prevent pathological aging, the most direct and effective way is to protect the skin from the sun, especially from direct ultraviolet radiation.