The appearance of one centimeter of pubic hair in a ten year old girl may be normal or it may be precocious. The onset of sexual development is not exactly the same for different girls. Generally speaking it is normal for girls to start their sexual development after the age of eight. Under normal circumstances, when a girl’s sexual development begins, the earliest phenomenon is the enlargement of breasts, and then pubic hair begins to appear. If a girl’s breasts begin to develop after the age of eight, and then pubic hair begins to appear, it is normal for one centimeter of pubic hair to appear by the time she is ten years old. If a girl’s breasts begin to develop before she is eight years old, and a large number of one-centimeter pubic hairs appear by the time she is ten years old, this is often a case of precocious puberty, and it is important to take your child to a doctor to find out the cause of the problem and then take the appropriate treatment measures.