Your period is a part of the menstrual cycle, which, for most people, lasts 28 days. “During your period, you shed the endometrium – the lining of your uterus,” explains Sarah Welsh, a gynaecologist and founder of the sexual wellness brand HANX.

“The menstrual cycle is regulated by hormones (progesterone and oestrogen), which are released by the ovaries, and these hormones cause the lining of the uterus to build up,” Welsh explains. “The thick uterine lining is primed for a fertilised egg to implant into, but if there is no fertilised egg then the uterine lining breaks down and bleeds out of the vagina.”

Because you only bleed if an egg hasn’t been fertilised (which is the start of a pregnancy), this is why a period is a good indicator that you aren’t pregnant.

“Why is my period so heavy this month?”