What skin temperature feels comfortable to you? I'm not talking about air temperature, I'm talking about the temperature of your skin itself, under your clothes. Chances are, it's about 86 degrees Fahrenheit.

If your skin gets much hotter you start to sweat.  If your skin gets colder, you'll probably reach for a sweater.  On today's Moment of Science, we'll learn about skin's built-in thermometer.

Skin has two types of cells for measuring temperature:  heat receptors and cold receptors.  These are scattered over your whole body, but they're most heavily concentrated on your face, your most temperature-sensitive region. Your brain determines skin temperature by counting how frequently these cold and heat receptors fire.

If you've ever spilled something very hot on yourself, you might have noticed that it can feel oddly chilly in addition to painfully hot. This is because your cold receptors start firing at very high temperatures, as well as your heat receptors. 

Likewise, if you touch something very cold, it might feel strangely hot as well. This is because pain receptors are triggered by extreme cold, and these signals are easily confused with heat.

If your skin's only a little hot or cold, but still near 86 degrees, your receptors will stop firing, and skin will get used to being that temperature. You can test this by filling three bowls of water: make one warm, one cool, and one in between. 

Put one hand in the warm water and the other in the cool, then leave them there. After they get used to these temperatures, move them both to the middle bowl. Your hand from the cool water will now feel warm, while your hand from the warm water will now feel cool!