Menstruation is a natural cycle where the uterine lining sheds, resulting in a flow of blood and tissue over several days. When people submerge themselves in water, such as a bathtub, pool, or ocean, they often report that their flow seems to vanish. This leads to the widespread belief that water somehow pauses the biological process. This article explores the physics behind this perceived stop and offers practical advice for water activities during a period.
The Mechanism: Why Flow Seems to Stop
The feeling that your period stops in the water is a trick of physics, not a biological change. The body continues to shed the uterine lining regardless of external conditions. The primary reason for the temporary cessation of flow is hydrostatic pressure—the pressure exerted by the surrounding water on the body. This external pressure counteracts the force of gravity that normally pulls menstrual fluid downward.
When fully submerged, water pressure prevents fluid from actively flowing out of the vaginal opening, creating the illusion that the period has ceased entirely. If you cough, sneeze, or strain your abdominal muscles, the internal pressure might temporarily overcome the surrounding water pressure, allowing a small amount of fluid to escape.
Hygiene and Practical Advice for Water Activities
Engaging in water activities while menstruating is completely safe and hygienic. Concerns about water contamination in a pool are unfounded, as the chlorine or bromine in treated water neutralizes bacteria and other microbes. The amount of blood that might escape is minimal and instantly diluted.
To manage flow and prevent leakage, internal menstrual products are the most effective choice. Tampons and menstrual cups work well because they collect the fluid before it can exit the body. Menstrual cups are particularly advantageous as they collect rather than absorb fluid and do not take in the surrounding water.
Pads and panty liners are not suitable for water activities because their absorbent material quickly becomes saturated with water, rendering them ineffective. If using a tampon while swimming, change it immediately after exiting the water to maintain comfort and hygiene, as the material may have absorbed pool or sea water.
What Happens When You Exit the Water
The moment you exit the water, the hydrostatic pressure holding the fluid in place is instantly removed. Gravity immediately takes over, and the menstrual fluid accumulated during submersion is now free to exit the body. This sudden release can feel like a rush or a gush of blood, which may be mistaken for a temporarily heavier flow.
This sensation is simply the menstrual fluid catching up to its normal rate of flow, confirming that the period never truly stopped. Being prepared with a fresh tampon, cup, or other preferred product is helpful to manage this immediate return to flow.