Fine hair may be caused by physiological factors such as heredity and improper hair care, or it may be caused by diseases such as hypothyroidism and malnutrition. 1. Physiological factors: fine hair may be related to heredity, if both parents have fine hair, the child may also appear fine hair phenomenon. Secondly, if the hair is not properly cared for, there is too high a shampoo temperature, frequent dyeing and ironing, etc., it will also lead to fine hair. 2. Hypothyroidism: hypothyroidism can be caused by autoimmune diseases, pituitary diseases, thyroid destruction and other factors, including pernicious anemia, dyslipidemia, etc., the patient will have metabolic disorders, so that the scalp nutrient intake is insufficient, which leads to the phenomenon of fine hair. 3. Malnutrition: malnutrition is mostly caused by poor nutritional structure, partiality, picky eating and other factors, patients with insufficient nutritional intake will lead to zinc deficiency, iron deficiency in the body, resulting in fine hair. There are many reasons for fine hair, and it is recommended that patients go to a regular hospital as soon as possible after eliminating physiological factors to avoid delaying their condition.