Melanin has a protective effect on the skin and is widely found in the skin, mucous membranes, retina, soft brain membranes, gallbladder and ovaries. Melanocytes are glandular cells located in the basal cell layer of the epidermis and in the hair follicles of the skin that synthesize and secrete melanin. Melanin is formed by the reaction of tyrosine in immature melanin with tyrosinase, an enzyme that converts tyrosine into dopa pigment, which then undergoes a series of steps to become melanin. After melanin is formed, it is passed through melanocytes to surrounding epidermal cells, causing normal skin tone. It is due to the presence of melanin that the skin has color, but in this process, melanin formation is affected by more factors: 1. UV light: melanin protects the skin from UV light, so UV light exposure can stimulate melanocytes to synthesize more melanin; 2. Inflammatory response. Skin inflammation will consume reducing sulfhydryl and other compounds in the skin, these substances consumed on the melanocyte synthesis of melanin does not produce inhibitory effect, melanin will be synthesized more; 3, irregular life: stress, paranoia, lack of sleep and other bad habits, will also increase melanin synthesis; 4, endocrine disorders: especially menstruation and pregnancy process endocrine disorders easily, is the peak period of melanin production .