Hair growth on the tailbone is usually caused by increased androgens in the human body or congenital occult spina bifida. 1. Increase in androgens: Hair growth on the tailbone is usually a normal physiological phenomenon. After puberty, with the changes in hormone levels, secondary sexual characteristics appear, such as an increase in body hair, an increase in male beard, and an increase in female pubic hair. Tailbone hair growth is also a kind of body hair, also related to hormone levels, mainly related to androgen levels, if the level of androgen increases, it may make the vertebrae hair growth, if the androgen is low, usually will not appear. 2. Congenital occult spina bifida: Since it has not injured the spinal cord and spinal nerves, it usually does not form obvious signs or symptoms. It is most common in newborns. If it occurs in the caudal vertebrae, it may be characterized by abnormal hair clusters and birthmarks. Hair growth on the tailbone usually requires a visit to the hospital, where a doctor will determine the cause and treat the condition.