You may have low estrogen levels. Especially if it’s accompanied by a lighter-than-usual flow, or if you’re an avid runner, says New York-based functional medicine nurse practitioner Margaret Romero. Studies have found that excessive exercise can lower estrogen levels, which can subsequently mess with your period, sometimes causing it to disappear altogether. (It’s not uncommon for female professional athletes to stop ovulating.)

While this may not seem like a big deal (who hasn’t fantasized about never having to deal with a period at least once or twice?), low estrogen levels can increase your risk of osteoporosis if left untreated. So if you’ve recently started training for a marathon, have started working out for the first time in your life, or have upped the intensity of your workouts and you notice that your periods are suddenly lighter in color and flow or less frequent, talk to your doctor.

Romero says other potential culprits of a pinkish flow can include poor nutrition, polycystic ovary syndrome (PCOS), or perimenopause, which is when your ovaries start producing less estrogen in preparation for menopause (generally, it occurs around four to five years before menopause).