What name is given to the onset of menstruation in human females (or girls)? At what age does this occur?

The onset of menstruation in human females is called menarche, which marks the first menstrual period and signals that a girl has reached reproductive maturity. Menarche represents a significant milestone in pubertal development, indicating that the hormonal systems regulating the reproductive cycle have matured sufficiently to support ovulation and potential pregnancy, though early menstrual cycles are often irregular and may not involve ovulation (anovulatory cycles) for the first year or two.

Menarche typically occurs between ages 10 and 16, with the average age being around 12-13 years in most populations, though this can vary based on several factors. Genetic factors play a significant role—girls often begin menstruating at ages similar to their mothers and sisters. Nutrition and body weight are also important; adequate body fat percentage (typically around 17%) is necessary for menarche to occur, which is why female athletes with very low body fat or girls with eating disorders may experience delayed menarche. Geographic and ethnic variations exist, with girls in developed countries generally experiencing menarche slightly earlier than those in developing nations, likely due to better nutrition and healthcare. Socioeconomic factors, overall health, and even psychological stress can influence timing. The age of menarche has gradually decreased over the past century, probably due to improved nutrition and living conditions. Menarche usually occurs 2-3 years after the first signs of puberty (breast budding) and near the end of the adolescent growth spurt. While the onset of menstruation can be emotionally significant, proper education beforehand—explaining what to expect, how to manage periods, and that this is a normal, healthy process—helps girls approach menarche with confidence rather than anxiety. Early or late menarche (before age 9 or after age 16) may warrant medical consultation to rule out underlying conditions.