In girls, pubic hair begins to grow, followed by underarm hair; breasts develop, with the areola around the nipple becoming darker. Fat deposits around the hips and buttocks also contribute to the female's more rounded appearance. Although the menstrual cycle begins, it may be irregular, with some monthly cycles occurring without ovulation. Since 1840, menstruation has been beginning a few months earlier every decade, possibly due to better nutrition or to the consumption of meat that contains hormones. In general, girls gain less height and weight than boys do during their teenage years.