Diving while on your period — what the research actually says

In one paragraph

Yes, you can dive while on your period — and nothing links menstruation to shark attacks. For decompression illness, a few studies suggest a possible link (especially for women on the pill), but none has proven it. The shark myth in particular has been investigated and dismissed (sharks detect blood at all of ~1 part per billion, but human menstrual blood is not biologically interesting to them — see International Shark Attack File. DAN's advice: diving is fine, a little more cautiously (shallower, shorter dives, longer stops), especially if you are on the pill. Practical management: tampons, menstrual cups, or period underwear under your wetsuit; cramps may make you want to sit out, which is also fine.

The shark myth, and the decompression question

Myth 1: sharks are attracted to menstrual blood. Sharks can detect blood at extraordinarily low concentrations — but menstrual blood is composed mostly of endometrial tissue, not the type of blood proteins that attract predator sharks (which respond to wounded-fish blood). The University of Florida's Shark Attack File explicitly states there's no evidence menstruation increases risk. What about decompression risk? Not proven either way. A DAN review of 956 women treated for DCI found many were menstruating at the time, especially those on the pill, but it had no comparison group; a 2003 study (Lee et al.) found more cases in the first week of the cycle. DAN's reading: a possible link, not proven. Hormonal contraception is not a dive contraindication. Full sources in our article on women, physiology and dive computers.

Practical management on a dive trip

Tampons or menstrual cups work fine under a wetsuit; either lasts a typical dive comfortably. Cups are the lower-environmental-impact choice (no waste). Period underwear (Thinx, Modibodi, etc.) works under wetsuits but adds bulk on the dive trip if you bring multiple pairs. Bring more than you think — laundry on Gili Air takes 24-48 hours. Painkillers (ibuprofen, paracetamol) before a boat ride if cramps are bad. If you have heavy cramps, sitting a day out is sensible — fatigue and concentration both matter underwater.

Common questions

Will the dive instructor know?

Only if you tell them. There's no visible sign once you're in a wetsuit. We'd rather know if you're fatigued or in pain so we can adjust the dive (shallow profile, shorter time) — but we never need the specific reason. "I'm a bit off today" is enough information.

I have very heavy periods. Should I skip the dives that day?

It's a personal choice. The comfort question matters most here. If heavy bleeding plus the boat ride plus the wetsuit means an unpleasant day for you, take the day off and snorkel from the beach instead — Gili Air's shallow reefs are world-class snorkeling and require no boat. The dive credit holds for the next day.