Diving while on your period — what the research actually says

In one paragraph

Yes, you can dive while on your period — and there is no peer-reviewed evidence linking menstruation to either decompression illness risk or shark attacks. 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](https://www.floridamuseum.ufl.edu/shark-attacks/reduce-risk/menstruation/). DAN's position: dive as normal. Practical management: tampons, menstrual cups, or period underwear under your wetsuit; cramps may make you want to sit out, which is also fine.

The two myths, dissected

**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. **Myth 2: hormonal changes increase decompression illness risk.** A 2002 DAN study of 1,000+ female divers found no statistical correlation between menstrual cycle phase and DCI incidence. Hormonal contraceptives, similarly, are not a dive contraindication.

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 medical risk doesn't change; the comfort risk might. 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.