Think back to middle school. If your experience was anything like mine, this is when your friends first started talking about periods. Except they didn’t speak about periods in the grown-up, sophisticated way many of us do now, using medically-correct words like vagina, vulva, and menstruation. Instead they giggled and whispered, using silly euphemisms like, “I’m on my ‘dot-at-the-end-of-the-sentence!’”
Even worse than the euphemisms were the myths. “I can’t run today,” one friend told me. “You can’t exercise when ‘Aunt Flow’ is in town.” Another told me bears can smell the period blood, so don’t ever go camping when you’re on your period.
Some of the myths surrounding menstruation are downright silly, and easy to dismiss once we grow a little older and wiser. But others are more complicated — maybe it really is worse to exercise when menstrual cramps are already beating up your insides.
Below, we explain what the experts and research really says about 8 common period myths.
Your period will sync with your friends’
Although almost anyone who has a period can recount a time when their menstrual cycle “synced” with a roommate or friend’s, the idea that periods sync up isn’t backed by solid science, according to the Cleveland Clinic.
The myth of syncing seems to stem from a 1971 study in the journal Nature, which looked at 135 women in a college dormitory and measured when each woman’s period would start. Seeing “a significant increase in synchronization of onset dates,” the study’s author theorized there might be something phermonal going on.
More recent studies, however, haven’t been able to replicate these results, nor find any biological reason one person’s period would intentionally match up with another’s. In fact, a 2006 study attempting to replicate the 1971 paper’s results (again studying women living in dorms), found that the 186 women in their sample did not sync up. More tellingly, the researchers revisited the 1971 data and found that any syncing was actually the result of chance.
So when it feels like biology has purposefully made you sync periods with your roommate, best friend, sibling, or partner, either pairing you with a perfect commiseration partner or getting the misery over in one fell swoop, what really happened is purely math. Mathematically speaking, since menstrual cycles aren’t a perfect, regular 28-days for everyone, your period will eventually cross over with that of anyone else in your house who bleeds.
Periods attract sharks and/or bears
While this one might seem too ridiculous to even warrant debunking, it actually has basis in history. According to the National Parks Service, two women camping separately were attacked by grizzly bears in Glacier National Park on August 13, 1967. Following the attacks, there was speculation that the bears were attracted to these women by the smell of menstrual blood.
A similar myth follows sharks. You may have heard from friends growing up, or from The Cosby Show on Nick at Night (like I did) that sharks can smell period blood — so stay far away from the ocean when you’re on your period.
Yet, there’s no scientific evidence that either animal will sniff menstrual blood and think, “mmm, dinner!”
Studies that analyzed hundreds of grizzly bear attacks found no correlation with menstruation, and a study that recorded the responses of 26 black bears to both menstruating women and used tampons found that the bears had no attraction to period blood. Further analysis of bear attacks in Yellowstone National Park between 1979 and 2018 found that of 50 attacks, 78% were on men, and of the 11 women who were hurt in bear attacks, most wandered into the bear’s path on a hike (and the attack had nothing to do with menstruation).
The same is true of sharks. While sharks do have impeccably good noses (able to sniff out blood at one part per million, according to the American Museum of Natural History), there’s no evidence they’re attracted to period blood.
For one thing, menstrual blood isn’t the same as blood from other parts of your body. It’s a mix of blood, vaginal fluid, and the cells and fluid from the endometrial lining. It’s also not the same as seal’s blood, which is much more likely to attract a shark who likes to eat seals (not people).
According to the Florida Museum, roughly 80% of recorded shark attacks happen to men, mostly because men are more likely to do sports that put them in the path of sharks (surfing, diving, and spear fishing). Yet, as more women and gender nonconforming people have taken up these sports, there has been no uptick in shark attacks.
You can’t take a bath when you’re on your period
Like many period myths, this one lies firmly in the “ew factor” associated with period blood. Some people consider taking a bath when you’re on your period to be unhygienic because blood can leak out and “infect” the bathwater.
But there’s no real safety risk in taking a bath during your period. John’s Hopkins Children’s Hospital says that blood won’t even leak out most of the time, but if it does “it’s not a big deal.” And the Mayo Clinic actually recommends a hot bath when you’re menstruating. The heat of a bath surrounding your abdominal muscles may be just as effective at relieving menstrual cramps as over-the-counter painkillers, according to the clinic.
So go ahead, turn on the tap, pour in some bubble bath, and sink into the water.
Your period will stop when you go swimming
This is one myth that’s actually semi-true. As John’s Hopkins said about baths, most of the time, period blood won’t even leak out.
That’s because the pressure water puts against the vaginal opening where period blood comes out is often enough to counteract the gravity pulling the blood out when you’re above water. Water pressure is your friend when you want to go swimming without a tampon or menstrual cup.
However, what the myth gets very wrong is that swimming doesn’t stop your period. Even while in the water, you’re shedding your endometrial lining and it’s got to go somewhere. If you cough, sneeze, or move around too much the pressure will change and you will leak small amounts of blood into the water. And when you get out, the blood will start flowing again.
Periods make you moody
We’ve all heard the barb: “Must be that time of the month.” A common phrase that’s often used to dismiss someone's valid feelings of anger or frustration.
First, let’s address the truth: PMS is a very real medical condition that affects many people who have periods. And it can cause dips in mood that sometimes look like depression or irritability, according to Planned Parenthood. So yes, periods can make you “moody.”
But let’s go back to that line above — one too many of us have heard from our brothers, male friends, partners, and fathers. PMS is not to blame for every strong emotion we have, and certainly not valid anger. Too often, menstrual cycles are used to brush aside womxn’s anger. We have a right to be angry.
Period sex is unhealthy
This is another one that stems deep into the “ew factor” of period blood. Cisgender men interviewed about period sex in the 1930s and 40s said they had learned from friends that sex with someone who was menstruating was not only unsanitary, but would also cause their penises to fall off. More recently, a 2009 study which interviewed 108 women and 12 men found that of those who were sexually active, about half of women said they would never have sex while on their periods. Yet most sexually active men (7 out of 9) said they would have sex with someone who was menstruating.
Over the years, it seems cisgender men have learned that no, your penis will not fall off if it touches period blood. But there does still seem to be some disgust, and possibly shame, around period sex for cisgender women.
We know, however, that there is nothing unsanitary about period sex — and as long as everyone involved consents, it’s perfectly safe. In fact, starting in the 1960s, sex education literature made it clear that period sex is totally fine. A 1962 guide stated, “having intercourse even during menstruation can be comforting and good,” according to The Modern Period: Menstruation in Twentieth-Century America.
Later guides even started explaining the benefits of period sex. Far from being unhealthy, period sex, especially sex that ends in orgasm, can be very helpful in relieving the pain of menstrual cramps!
You can’t (or shouldn’t) exercise when you’re on your period
If you, like me, had friends use the period excuse to try to get out of gym, you might start thinking they had a point. How did those gym teachers expect us to run a mile or play volleyball or soccer with menstrual cramps tearing up our insides?
Well, turns out the gym teachers were right — periods are no real reason to skip out on exercise. Research has found no difference in menstruating people’s ability to exercise when they’re on their periods vs. not, according to the U.S. Department of Health and Human Services.
In fact, some research has suggested that people get fewer menstrual cramps when they exercise regularly. So there’s a chance choosing not to skip your run when you’re on your period could actually make you feel better. However, exercising too much can lead to missed periods or can cause your period to stop altogether. Irregular or missing periods are common in athletes who work out hard, but suddenly starting a vigorous exercise routine when you haven’t been working out before could also lead to missed periods. Be sure to talk with your doctor if this happens to you to make sure you’re exercising safely.
Periods are just for women
This myth is as outdated as the gender binary it’s based on. As celebrities like J.K. Rowling insist that only women bleed (by which they mean only cisgender women), they ignore the bodies and experiences of transgender men and nonbinary people who have uteruses. All bodies and all genders are valid, and everyone who experiences menstruation deserves recognition and respect for what their body goes through.
Kasandra Brabaw is a freelance writer and editor with focus on health, sex, and LGBTQ+ identity. You can find her work at Health, Bustle, Women's Health, Allure, and other publications.