Dear Alice,

Why does a woman have loose stools during a menstrual cycle?

Dear Reader,

Not only can women experience cramping, bloating, and feeling lousy during their period — sometimes they have the pleasure of other symptoms like loose stools. While many women experience few or no PMS symptoms, for some, PMS symptoms are enough to make a person wonder why human bodies can be so cruel.

There may in fact be a physiological link between menstruation and diarrhea. Shortly before a woman's period begins, the cells forming the lining of the uterus begin to produce more prostaglandins. These hormone-like compounds perform a variety of functions including stimulating the smooth muscles in the uterus to contract and expel the accumulated uterine lining. During menstruation, the cells lining the uterus breakdown and release large amounts of prostaglandins to slough off and expel the uterine lining. If the body makes more prostaglandins than it needs, a woman is likely to experience stronger cramping and perhaps pain during her period (because larger amounts of prostaglandins will cause the uterus to contract more strongly). An additional side effect of producing too many prostaglandins is that some may enter the bloodstream and travel throughout the body. Since the bowels are lined with smooth muscle, excess prostaglandins may also cause diarrhea by stimulating the large intestines and bowels to contract and expel their contents. Excessive prostaglandins could also cause headaches, nausea, and vomiting. What fun!

It is helpful to know that there are no dangerous health consequences if the body makes too many prostaglandins, besides the discomfort that may be experienced. The symptoms of excess prostaglandins (abdominal pain, loose stools, etc.) may be relieved by resting, using a heating pad on the lower abdomen or back, eating a well-balanced diet, getting moderate exercise, and/or taking medications that relieve swelling — like ibuprofen. Hopefully one of these solutions results in a more comfortable period next month!

Best Wishes,


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