After half an hour in water, why do fingers and toes become wrinkly?

bathroomTo understand what’s going on, you need to know a little anatomy according to Dr. Karl Kruszelnickl in Great Moments in Science.

“First, the skin of your fingers and toes has one of the highest densities of sweat glands anywhere on your skin.

Second, the skin of your fingers and toes are indeed work areas. The outer layers of the skin sit on the inner layers like sheets of corrugated iron, so that when you grab something, the different layers don’t slip over each other. In fact, not only are they corrugated, the upper and lower layers are also tethered to each other, at intervals of about a millimetre.

And third, there are special organs in your fingers and toes called ‘glomus bodies’, which are involved in both sensing temperature, and then regulating temperature. A typical glomus body is about 0.25 — 0.5 millimetres across, communicates mostly via sympathetic nerves, and has arteries running directly into veins. If glomus bodies let the warm blood run directly from the artery into the vein, the warm blood heads back to the heart and the fingertip cools down. But if they don’t let the warm blood take a short-cut, and instead, force it to perfuse through the fingertip, then the fingertip warms up.

So here are the five steps of Dr Wilder-Smith’s theory. It’s still a theory in the sense that not all, but most, of the steps have been proven or observed.

First, thanks to the huge numbers of sweat glands, water easily permeates into the skin of the fingers and toes.

Second, this water locally dilutes the normally tightly-regulated levels of salts in the skin.

Third, these diluted levels decrease the stability of the cell membranes in the local tissues, and leads to increased firing rates of the dense networks of sympathetic nerve fibres. These sympathetic nerves help control the diameter of the blood vessels in the fingers and toes, and when they fire off, they close down these blood vessels – both the regular blood vessels and those in the glomus bodies.

Fourth, now that the blood vessels in the fingers and toes are partially closed down, the volume of the fingers and toes shrinks.

Fifth and finally, this shrinking is uneven due to the roughly millimeter spacing of the “tethering” of the different skin layers. And that’s how you get aquatic wrinkling.”

From:   © 2014 Karl S. Kruszelnicki Pty Ltd  Published 22 January 2013