Long sweat hair in girls may be caused by physiological factors such as heredity, or by diseases such as hirsutism and polycystic ovary syndrome. 1. Physiological factors: Heredity, androgen secretion and other factors may trigger hair growth, and some women may experience long hair. 2. Hirsutism: The cause of hirsutism is complicated, and may be related to endocrine, genetic and external stimuli, etc. Women with hirsutism often show a large number of long and thick hairs in areas that should not have hair. 3. Polycystic Ovary Syndrome (PCOS): Heredity, environment and other factors work together to trigger the disease, which usually manifests itself in obesity, acne, menstrual disorders, hairiness and infertility. There is no single cause of long sweat hair in girls. After eliminating physiological factors, patients are advised to seek medical examination to clarify the cause of the disease.