It usually takes 2-2.5 years for breast development to lead to menstruation. Breast development: As girls grow older, their breasts gradually enter a period of development. Between the ages of 8 and 12, the body begins to release sex hormones, fat accumulates in the subcutaneous tissue of the chest, breast development occurs, and girls develop feminine characteristics. 10-17 years old, secondary sexual characteristics gradually develop and mature, and begin to be accompanied by menstruation. Menstruation: The first menstruation is called menarche, which is a sign that a girl has entered puberty, and it usually occurs between the ages of 12 and 15, while menarche at the age of 11 and 16 is also normal. When menarche comes, girls grow rapidly, breasts develop and bulge, nipples have pigmentation, areola area becomes larger. Parents should counsel girls on women’s health and teach them about sexual physiology and psychology to avoid aggravating the child’s psychological burden. If there is any discomfort, consult a doctor in time.