If you hold a piece of dry ice too long, it feels like it is burning your skin. Your skin isn't actually burning, though. What is actually happening is that the dry ice is freezing your skin. The dry ice is carbon dioxide that has been frozen at -110 °F (-79 °C). That's why it hurts when you hold it too long, because your skin is starting to freeze from its cold. Freezing skin is a bad thing, so I recommend not letting dry ice ’burn’ you.
The reason that freezing and burning can feel the same is because touching things that are very cold can do the same thing to your cells as touching things that are very hot. The burning feeling comes from some of your skin cells being damaged and breaking open. This happens when the cells’ membranes are broken open. (You can think of the cell membrane as the wall of the cell.) If you touch something hot, some of the cell membranes are actually melted, breaking the cells open. If you touch something very cold, the water in your cells turns into ice, forming crystals that can tear through the cell membranes. In either case the result is the same - the cells are damaged. This is what you feel.
I hope this answers your question.
(published on 07/28/11)
(published on 08/21/07)