In high school, I would occasionally skip school when I had my period to spend the day hanging out in my bathtub. I mostly did it because I preferred bubbles and bath bombs to physics class — but I’d also heard a rumor that being submerged in water could stop my menstrual flow in its tracks. Yes, really stop it. Like the Christmas ceasefire during World War I or like Bruno Mars before he filled his cup with liquor in “Uptown Funk.”
But, as it turns out, I was just buying into one of many myths abound about menstruation. “It is a very common misconception that a woman’s period will stop when she gets into the water, and that is not the case,” explains Temeka Zore, MD, OB/GYN, a reproductive endocrinologist at Spring Fertility. “While I don’t know the origins of this myth, I imagine it has been perpetuated through the years due to this being a common experience many women notice while they are underwater."
The reason you may think you’re no longer bleeding whilst in the tub has to do with buoyancy. Yes, the scientific phenomenon that allows something to float or sink, also known as upthrust. Buoyancy creates upward force that’s exerted on objects submerged in fluid. It’s the reason you have to keep paddling hard to stay at the bottom of the deep end to collect pool rings. It’s not magic, but physics. (Hey, I didn't skip every day.)
“The pressure of the water can make it so the blood doesn't actually flow out of the vagina [or genitals],” explains Jennifer Linhorst, MD, OB/GYN, who's based in Colorado. But you should still plan on wearing a tampon or menstrual cup to swim. Pads are made to absorb blood — that means they'll also absorb water, which wont' make for a comfortable dip in the pool.
"A cough or sneeze might overcome some of that pressure, allowing some [blood] to escape, perhaps especially if someone has a heavier flow,” Dr. Linhorst says. “It wouldn't be very noticeable in the water, but could still cause staining of one's swimsuit.”
Dr. Zore adds that once you get out of the water, the bleeding will resume.
There are plus sides to splashing around on your period. Hot baths can stimulate blood flow, which can ease cramps, according to Mayo Clinic. Plus, swimming in a pool or even jumping along with the waves in the ocean can be a form of exercise, which research has shown can reduce menstrual aches and pains. So feel free to spend some extra time submerged during your time of the month — it may not shorten your cycle, but it can make it less uncomfortable, which is a win.