Most of us have jumped into a swimming pool and felt the shock of the cold water, only to have it feel just fine after a minute or so. Or, we've stepped into a nice warm shower and after a minute reached over and turned up the heat a little because it was not feeling warm enough. Those who like hot showers might turn up the heat a couple of times before it suits them.
This ability of the body to adjust to temperatures is called thermal adaptation. When you adapt to a temperature it means it doesn't feel cold or hot, but neutral.
A simple experiment can clearly demonstrate thermal adaptation. Get three bowls large enough to put your hands in. Put cold water in one; you might add a few ice cubes to make the water cold. Put water that is hot, but not too hot to put your hands in, in the other. And in the third bowl water that is warm, about ninety degrees.
Put one hand in the bowl with the cold water, and the other in the hot water for about a minute. Now put both hands in the bowl of warm water. The warm water will feel very cool to the hand that originally was in the hot water, and warm to the hand that was in the cold water.
Understanding The Process
Fortunately thermal adaptation has its limits, because otherwise we might get burned or frozen if at some point the warning sensation of extreme heat or cold didn't override adaptation.
Scientists do not completely understand the process of thermal adaptation, but they've known about it for a long time. The first report of the experiment with the three bowls of water was given by the philosopher John Locke in 1690.