The earlier you begin your periods, the higher your risk, but this effect is small and gradual. Your risk of breast cancer will not dramatically increase if you start your periods just before 13 (the average age).
The increase in risk of breast cancer seen with early puberty is probably because these women are exposed to the female hormone oestrogen for longer than women who started their periods later.
Our fact sheet Puberty, menopause and breast cancer risk: The facts contains more information on puberty and breast cancer risk.
Information last reviewed: 1 November 2011
