You know how, if you spend a long time in the bath, your fingers go wrinkly? They end up looking like raisins!

Well, if you’ve got kids, they’ll have asked that question of you a million times. Want to know what the answer is?

Well, it’s said that our skin is covered in an oily substance called Sebum. When you’re in the bath for a long period of time, this protective film is washed away, leaving the skin on your fingers (and toes) free to absorb water. As they absorb the water, there’s nowhere else for the fluid to go, so your skin swells and buckles to create the wrinkly finger effect.

The process by which your skin absorbs water in the bath is called “Osmosis“. Water moves through a semi-permeable membrane (in this case, your skin) from one area of higher water concentration (the bath) to another area of lower water concentration (your body), and since there is a higher concentration of water in the bathtub than in your skin, the water will flow into the outermost layer of your skin, causing the cells that make up this layer to swell. In order to compensate for this increase in surface area, your skin wrinkles.