Acne on the chin of a 40-year-old woman is caused by endocrine disorders, polycystic ovary syndrome, bacterial reproduction and other reasons. 1. Endocrine disorders: the endocrine system can regulate human growth and development, metabolic processes, reproductive aging and other physiological activities, and when the endocrine disorders, the endocrine system in the body will be disrupted, and then there will be a variety of signs, 40-year-old woman may be caused by the phenomenon of chin acne. 2. Polycystic ovary syndrome: Polycystic ovary syndrome is a disease caused by metabolic and endocrine abnormalities, which can lead to acne. 3. Bacterial reproduction: 40-year-old female chin acne may be related to the reproduction of Propionibacterium acnes, mainly due to the bacterium is easy to reproduce in the hair follicles and other parts of the body, in the case of not paying attention to hygiene will be prone to the phenomenon of chin acne. It is recommended to go to a regular hospital for examination, the doctor will be based on clinical symptoms to give judgment, clear cause of the disease and timely symptomatic treatment.