You have a boat dive booked for Saturday. Your period arrived this morning, and you are typing the question into a search bar rather than asking anyone out loud. A fair question, asked in earnest. It deserves a sourced answer instead of a forum thread.
The International Shark Attack File has investigated more than 6,800 cases, covering the early 1500s to the present. Its position runs to a single sentence: there is no positive evidence that menstruation is a factor in shark bites. The same file records a ratio of about eight men bitten for every two women, so more than 80 percent of documented bites in history happened to men. A fluid that pulled sharks towards people would bend that ratio the other way.
Are sharks attracted to menstrual blood?
Detection and attraction are two separate claims, and the myth runs them together. ISAF is direct about the first one. Any bodily fluid released into the water is likely detectable by a shark, and menstrual blood sits in the same category as urine and anything else a body puts out. A shark passing by can register that something organic is present.
The second claim is where it comes apart. DAN Southern Africa states there are no data supporting the belief that menstruating women face a raised risk of a shark bite, and gives two reasons for it. The volume lost across a period is small and spreads over several days. Many shark species are not drawn to the blood and tissue debris in menstrual flow at all. Detectable is not the same thing as interesting.
How far can a shark smell blood?
Less far than the versions in circulation. ISAF describes a shark's sense of smell as powerful enough to locate prey from hundreds of yards away, which comes to a few hundred metres. That figure comes from the organisation keeping the database. The drop-in-an-Olympic-pool and mile-away claims repeated in lifestyle articles are not ISAF's, and ISAF does not state them anywhere.
Distance is also the wrong axis for the question. A shark registering something organic in the water is not a shark deciding to bite a person, and the gap between those two events carries the whole answer. Our article on what the shark bite records show for divers sets out the base rate and the circumstances behind it.
Does water pressure stop the flow while you are under?
ISAF says evidence suggests it does, temporarily. Its wording is that water pressure will temporarily stop the flow of menstrual blood while swimming, decreasing the chance that any blood reaches the water. Temporarily is the word doing the work there. It describes a pause under pressure rather than a seal, and it says nothing about the surface interval or the drive home.
Less enters the water than people assume, then, starting from a volume that was small already. A reduction applied to a reduction. That is worth knowing, and it is not the reason the myth fails. The bite record is.
Is it safe to dive on your period?
DAN Southern Africa's position is that diving while menstruating does not appear to be a problem, provided normal vigorous exercise does not worsen your symptoms. Where the week brings pain, heavy fatigue or anything else affecting your health, weigh that the way you would weigh a bad back. ISAF adds that many people dive while menstruating, and that it has recorded no obvious pattern of increased shark encounters among them.
ISAF also publishes the other half, and honest writing includes it. Someone trying to reduce every risk within their control could stay out of the water during menstruation, and ISAF lists that as a step available. It stops short of recommending it. The page records it as an option for a person who wants the number as near zero as it goes.
- Detection is not in dispute. ISAF states that any bodily fluid released into the water is likely detectable by a shark, menstrual blood included.
- Attraction is a different claim, and it fails. DAN Southern Africa points to the small volume lost across several days, and to the many shark species not drawn to the blood and debris in menstrual flow.
- The bite record gives it nothing. More than 80 percent of documented bites happened to men, across a file running back to the early 1500s.
- Decompression risk is the open question. Not the shark question.
Confined water sessions for a course run in the heated indoor training pool in Fourways, where the shark half of this question does not arise at all.
Does menstruation change decompression sickness risk?
This is the part with no settled answer, and the honest version is less comfortable than the shark half. DAN Southern Africa sets out a theoretical mechanism. Fluid retention and tissue swelling could leave a body less able to offload dissolved nitrogen. Its own next line says the idea is not definitively proven, and that is where the evidence stops.
Some numbers sit behind that sentence, and they are worth stating plainly. A retrospective review of 956 women divers who had decompression illness found 38 percent were menstruating at the time of the injury. Among those on oral contraceptives, 85 percent were menstruating when the accident happened. DAN Southern Africa reads that as suggesting, without proving, a raised risk during menstruation for women taking oral contraceptives. Four further studies have produced evidence of higher decompression illness risk in women, and one study of altitude bends found menses appearing as a risk factor.
Read that as neither clearance nor warning, because it is neither. An association found by looking backwards at injured divers is not a cause. DAN Southern Africa's practical suggestion is conservatism rather than avoidance: fewer dives in a day, shorter and shallower profiles, longer safety stops, and reduced exposure for women on oral contraceptives. The mechanism being made more conservative sits in our article on how decompression sickness happens. Your doctor is the person to take the oral contraceptive question to.
Why does the myth keep coming back?
The sex ratio looks like evidence until you read the explanation beside it. ISAF is explicit that sharks do not prefer to bite men. The 8:2 split reflects who has historically been in the water doing the higher-exposure things, surfing and spearfishing and long-distance swimming among them. ISAF also reports that the share of women bitten has risen as more women take up water sports, which is what exposure would predict and blood would not.
The rest is repetition. The claim costs nothing to publish and takes work to check, so period-product pages and lifestyle sites carry it, each one citing the last. The organisation that keeps the file has published the opposite for years and sits below them in the results. That is a ranking problem rather than a scientific one.
Sources
- International Shark Attack File: Menstruation and Sharks. The statement that there is no positive evidence menstruation is a factor in shark bites, the eight-to-two sex ratio, the water pressure note and the risk-reduction wording.
- International Shark Attack File. The scale of the database: more than 6,800 individual investigations covering the early 1500s to the present.
- DAN Southern Africa: Menstruation During Diving Activities. The theoretical decompression illness mechanism, the 956-diver review, the oral contraceptive finding, and the shark answer.
Frequently Asked Questions
Do sharks smell period blood?
A shark can detect any bodily fluid released into the water, menstrual blood among them. The International Shark Attack File states there is no positive evidence that menstruation is a factor in shark bites, and DAN Southern Africa reports no data supporting a raised risk.
Can you scuba dive with a tampon in?
Neither ISAF nor DAN Southern Africa singles out any menstrual product, because the question they answer concerns fluid in the water rather than what contains it. Use what you use on land and are comfortable wearing for the length of a dive.
Does water pressure stop your period while diving?
ISAF states that evidence suggests water pressure temporarily stops the flow of menstrual blood while swimming, reducing the chance any blood is released. Temporarily is the operative word, and it says nothing about the surface interval.
Are women bitten by sharks more often than men?
No. ISAF records about eight men bitten for every two women and attributes the split to historic exposure rather than preference. The share of women bitten has risen as more women take up water sports.
Does diving on your period raise decompression sickness risk?
The question is unresolved. DAN Southern Africa describes a theoretical mechanism involving fluid retention and tissue swelling, and states it is not definitively proven. It suggests more conservative diving during menstruation, particularly for women on oral contraceptives.
Should you skip a dive during a heavy period?
DAN Southern Africa's line is that menstruation on its own is not a reason to sit out, provided vigorous exercise does not worsen your symptoms. Pain, heavy fatigue or anything else affecting your health that week is a reason to speak to your doctor first.
This is general information, not a substitute for a dive medical or advice from a doctor trained in dive medicine. In an emergency, contact your local emergency services and DAN Southern Africa on +27 82 810 6010.
Reviewed September 2026. Devon Ford runs Scuba Evolution, a PADI 5 Star Dive Centre in Glenvista, Johannesburg.
