In general, hair can grow 0.27-0.4mm in length a day. Most of the human hair is in the stage of growth, and the growth has a certain regularity. The main factors affecting hair growth are race, gender, age, genetics, endocrine, mental state, disease, etc., so there will be some individual differences in hair growth. 1, race: different races, different hair color, the number and growth of the situation is different, in the Caucasian, baldness is often more common; 2, gender, age: in general, hair growth faster than men, young people faster than the elderly; 3, genetics: in the same family, the hair growth rate of women than men. Young people are faster than the elderly; 3, genetic: in the same family, often hair growth will be roughly the same; 4, endocrine: androgens themselves can act directly on the hair follicles, such as androgen excess can lead to slow hair growth. If androgens are normal or reduced, it will not affect the hair growth rate. In addition, insufficient thyroid hormone, low adrenal function and hypopituitary function can lead to slow hair growth; 5, mental state: if long-term tension, fear and anxiety, hair growth will slow down, or even cause hair loss; 6, disease: if there is anemia, liver disease and serious chronic wasting disease, so that the body is in a state of malnutrition, the human body’s Vitamin A and B and the lack of zinc, iron, magnesium, calcium and other substances will affect the growth rate of hair. If the content is normal, the hair growth rate is also normal, such as the lack of vitamins and trace elements in the body, it may lead to slow hair growth; 7, other: summer compared to winter, daytime compared to night, hair growth is faster. Some chemical factors, ultraviolet rays, drugs, trauma and skin diseases also have an effect on hair growth.