Every 28 days, your body produces a hormone-like chemical named prostaglandins, responsible for causing uterine contractions and pushing out the endometrium (uterus lining) each month.
Prostaglandins can also enter your bloodstream and interfere with the lining of your intestines which can cause bowel disturbances and diarrhoea in the days leading up to your period. Prostaglandins can also reduce food absorption in your gut, which means food passes through your colon faster, resulting in loose stools or diarrhoea.