Nine Period Myths, Debunked
Nine period myths, from sharks and bears to synced cycles and lost tampons, checked against what the evidence actually shows.
Published 27 July 2026
Sharks, bears, synced cycles, lost tampons. Period myths like these spread because they are memorable, not because they are true. Here is what NHS guidance, wildlife biologists and published research actually say about nine of the most repeated ones.
Myth: Sharks are drawn to period blood
Reality: there is no evidence that period blood attracts sharks. The International Shark Attack File is maintained by the Florida Museum of Natural History. It has tracked shark bites for decades and found no positive evidence that menstruation is a factor. More than 80 per cent of recorded shark bite victims have been men. The museum links this pattern to who spends more time in higher-risk water, not to menstruation. The same source notes that water pressure temporarily holds the flow back while you are submerged. That lowers the chances of any blood reaching the water in the first place.
Myth: Bears are drawn to period blood
Reality: no study has shown a link between menstruation and bear attacks. In 1967, grizzly bears in Glacier National Park killed a menstruating woman and a woman with tampons in her purse. Park authorities began warning that bears might be drawn to menstrual odour, and the idea stuck. But bear biologist Stephen Herrero later reviewed over 100 grizzly bear killings. The Glacier National Park victim was the only menstruating woman on record. The scare outlived the evidence.
Myth: Your period stops in water
Reality: your period does not stop in water. It is only held back temporarily by pressure. Swimming is safe on your period. The NHS lists swimming among the gentle exercises that can ease period pain, alongside walking, cycling and yoga. Water pressure temporarily holds the flow back while you are submerged. It resumes once you get out. Read more, including which products work best in the water, in our guide to sport and swimming on your period.
Myth: You cannot wash your hair on your period
Reality: washing, hair included, has no effect on your period. The NHS even recommends a warm bath or shower as one way to ease period pain. There is no medical reason to skip a wash because you are bleeding. Keeping up your normal hygiene routine, hair included, is entirely your choice. It is not a rule your period sets for you.
Myth: Exercise makes period pain worse
Reality: gentle exercise is one of the NHS's own suggestions for easing period pain. The NHS recommends movement such as yoga, swimming, walking or cycling. It suggests these alongside a warm bath, a heat pad and painkillers to help ease cramps. You do not have to push through a hard session if you are not up for it. Resting when you need to is fine too. But you do not need to sit out of PE just because periods are assumed to make you fragile. See a GP if period pain stops you doing your normal daily activities. Also see a GP if your periods become more painful, heavier or irregular.
Myth: Everyone can tell you are on your period
Reality: total blood loss across a whole period is small. Products are designed to be discreet too. The NHS puts average blood loss at around 20 to 90ml over an entire period. That is roughly 1 to 5 tablespoons, spread across several days, not one dramatic moment. A pad, tampon, cup or period underwear is designed to sit discreetly under clothing and manage odour. People notice far less than you expect, even on the days you feel most convinced they can tell.
Myth: You cannot get pregnant on your period
Reality: pregnancy on your period is possible, though less likely than at other times in your cycle. Ovulation usually happens 10 to 16 days before your next period. Cycles vary though, especially in the first few years, and sperm can survive inside you for several days. If your cycle is short or you ovulate early, sex during your period can still lead to pregnancy. If avoiding pregnancy matters to you, the NHS has clear guidance on choosing contraception. A GP, school nurse or another trusted adult can also talk it through with you, privately and without judgement. Our guide to pregnancy risk on your first period covers the timing in more depth.
Myth: Periods sync when you live together
Reality: the research does not support cycle syncing. The idea has been around for decades. But the strongest test of it does not back it up. Researchers Yang and Schank followed 186 Chinese women sharing dormitories for over a year. They found that women living in groups did not synchronise their cycles. The pair also reanalysed the original study behind the idea. The group synchrony in that data was no higher than chance, no more than random overlap would produce. Shared stress, shared routines and simple coincidence explain what looks like syncing better than any biological mechanism does.
Myth: A tampon can get lost inside you
Reality: a tampon cannot travel past your cervix, so it cannot get lost in your body. Your cervix, at the top of your vagina, is too narrow for anything solid to pass through. A tampon can sit high up or at an angle, so it can feel hard to reach. That can feel like it is "lost", but it is not. It stays exactly where you, or someone else, can reach it. If you cannot remove one yourself, a GP or sexual health clinic can remove it, quickly and without judgement.
The short version
Sharks and bears are not drawn to period blood. Water pressure holds a period back while you swim. It does not stop it for good. Washing your hair and exercising are both fine. Exercise can even ease cramps. People notice far less than you think from the outside. Pregnancy on your period is possible, if unlikely. Cycles do not reliably sync between people who live together. And a tampon cannot get lost, because it cannot pass your cervix.
If this is your first period, our complete first-period guide is the place to start.
Simply Track will not repeat any of these myths back at you. Period tracking, the calendar and every first-period guide in the app are free, always. Premium adds a daily Log, Insights and a doctor-ready PDF report for anyone who wants to go further. There is no account, no ads and no data sold. Everything stays on your device and, if you choose, syncs only to your own private iCloud. Its cycle predictions learn your rhythm over time, but like any prediction, they are estimates, never a form of contraception.
Sources
- Florida Museum of Natural History, International Shark Attack File, Menstruation and Sharks: https://www.floridamuseum.ufl.edu/shark-attacks/reduce-risk/menstruation/
- North American Bear Center, Myth: Menstrual Odors Trigger Bear Attacks: https://bear.org/bear-facts/myth-menstrual-odors-trigger-bear-attacks/
- NHS, Periods: https://www.nhs.uk/conditions/periods/
- NHS, Period pain: https://www.nhs.uk/symptoms/period-pain/
- NHS, Periods and fertility in the menstrual cycle: https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/
- NHS inform, Stuck or lost tampon: https://www.nhsinform.scot/healthy-living/womens-health/girls-and-young-women-puberty-to-around-25/periods-and-menstrual-health/stuck-or-lost-tampon/
- NHS, Contraception: https://www.nhs.uk/conditions/contraception/
- Yang Z and Schank JC (2006), Women do not synchronize their menstrual cycles, Human Nature: https://pubmed.ncbi.nlm.nih.gov/26181612/
Common questions
Can sharks smell period blood and attack because of it?
No. The International Shark Attack File has found no positive evidence that menstruation is a factor in shark bites. More than 80 per cent of recorded shark bite victims have been men, a pattern linked to who spends time in risky water, not to menstruation, and water pressure temporarily holds the flow back while you are submerged anyway.
Do periods actually stop when you get in a pool or the sea?
No, not permanently. Water pressure against your body temporarily holds the flow back while you are submerged, which is why it can feel like it has paused. It has not stopped for good. The flow resumes once you get out of the water, and this is completely normal.
Can you get pregnant if you have sex during your period?
Yes, it is possible, though less likely than at other points in your cycle. Ovulation timing varies, and cycles are often irregular in the first few years of having periods, so there is no fully safe day. Sperm can survive inside you for up to seven days, and contraception is the reliable way to prevent pregnancy.
Not medical advice
General information, not medical advice. If something about your cycle worries you, speak to a GP.
Keep track of your own cycle
Simply Track logs your period on your iPhone and Apple Watch, and its predictions sharpen the more you record. Your data stays in your own iCloud account.
