hypotonic cells in the swimming pool

[midwestnerd]

If swimming pool water is hypotonic to our cells and body fluid, then why don't we swell and pop after we go swimming?

[wildwood]

Are our cells not able to adjust their toning in water?

[dundurn]

Our skin is relatively waterproof - we have layer upon layer of dead cells sitting on top of the live cells underneath. On the other hand stay in water for long enough and you will absorb some, particularly on areas where the surface layer is relatively thin. The cells don't go pop because they're backed up by other cells underneath. As the outermost layer takes on water it becomes hypotonic relative to the cell layer immediately below which accordingly takes up a little of the absorbed water, and so on. A bit like bookmakers laying off bets!

It's this tendency to absorb some water from the surroundings that leads to the ridges on your fingertips if you have a particularly long bath.