Menstruation is the natural process of shedding the uterine lining, resulting in the flow of blood and tissue. When submerged in water, many people observe that this flow appears to slow down or stop completely. This temporary effect is not a physiological pause in the menstrual cycle, but rather a physical phenomenon caused by external pressure acting upon the body.
The Physics of Hydrostatic Pressure
The apparent cessation of flow is directly related to hydrostatic pressure, which is the pressure exerted by a fluid at equilibrium due to the force of gravity. When the body is submerged in water, the liquid exerts an external, uniform pressure on all surfaces, including the opening of the vagina. This external force effectively counteracts the internal pressure and the force of gravity that normally drive the menstrual fluid downward and out of the body.
Water is significantly denser than air, meaning it provides substantial resistance against the relatively weak flow of menstrual fluid. The pressure from the water temporarily holds the accumulated fluid inside the vaginal canal, preventing it from exiting the body. This effect is most noticeable when the person is still or swimming gently. Sudden movements, coughing, or sneezing can briefly increase internal abdominal pressure enough to overcome the external hydrostatic pressure, causing a small amount of fluid to escape.
Physiological Reality of Menstruation
While the external flow is suppressed, the internal biological process of menstruation continues without interruption. The uterus does not stop shedding its lining when submerged in water. Menstrual fluid continues to be released into the vaginal canal, where it accumulates until the external pressure is released.
This accumulation becomes immediately apparent upon exiting the water. When the hydrostatic pressure of the surrounding water is removed, gravity and internal forces immediately take over again. This causes the previously contained fluid to flow out normally. The perception that the period has “stopped” is merely a temporary physical illusion created by the surrounding environment.
Managing Menstruation During Water Activities
Using a reliable hygiene product is necessary when participating in water activities. External products like traditional pads or panty liners are not suitable for swimming. They are designed to absorb liquid and will quickly become saturated with pool or seawater, losing effectiveness.
Internal menstrual products are the most effective choice for water activity because they contain the flow internally, unaffected by external water.
Product Options for Water
- Tampons are a popular option, but they can absorb some water, necessitating a change shortly after exiting the water.
- Menstrual cups and discs are highly recommended alternatives, as they collect fluid with a seal rather than absorbing it.
- Cups and discs do not take in water and provide secure protection for up to 12 hours.
- Period-proof swimwear offers a modern solution for light to moderate flow, containing a thin, absorbent lining.
There is no scientific evidence to support the myth that menstruating in the ocean attracts sharks. Safety concerns regarding aquatic life are unfounded.