Dr. Craig Heller

Well, first of all, you get a tremendous shock.

And what that's going to translate into is a bit of a shot of adrenaline.

And I think this is really the so-called benefit, but it doesn't necessarily translate into any benefit in terms of your physiology or performance and so forth.

Now, if you take a cold bath or a cold shower, a couple of things are happening.

One is you're going to stimulate vasoconstriction.

So if anything, it's going to make it a little bit more difficult for your body to get rid of heat because you're shutting off your avenues of heat loss.

If you're in a true cold bath, the overall surface area of your body is so great that it doesn't matter if you've acid constricted, you're still going to lose heat.

The primary sites of heat loss, which we're going to get into, are the palms of your hands, the soles of your feet, and the upper part of your face.

And the reason these are avenues for heat loss is they're underlain by special blood vessels.

And these blood vessels are able to shunt the blood from the arteries, which are coming from the heart, directly to the veins, which are returning to the heart, and bypassing the capillaries, which are the nutritive vessels, but high resistance.

So you can tell when you shake someone's hand what his or her thermal status is.

The hand's hot or it's cold.

Well, there are differences that are more physical than anything else.

So if you are in a cold bath and you're still, you develop a boundary layer.

It's best to explain it in terms of a hot bath because everybody's experienced that.

You get into a hot bath and, oh, my God, it's really hot.

almost painful.

And then you sit down and eventually it doesn't feel so hot anymore because the still water, which is close to your skin, is coming into equilibrium with your skin.

So it's like having a blanket on you or an insulator on you.

And then if you move around, you disturb that still water layer, you feel the hot temperature again.