Question: What actually makes the salt and ice challenge hurt? salt and ice challenge= when you put a pile of salt onto your body, then put an ice cube on top, it then starts to burn

Austin Elliott answered on 14 Jun 2012:

Ouch. Sounds nasty.

One reason it hurts is that your skin contains many cells, basically specialised sensory nerve cells, that sense temperature. They do this by having special proteins in the cells’ membranes that change their activity with temperature, acting as kind of hot or cold ‘receptors’. This will activate the cell the protein is in to send a nerve signal back to the brain that registers as ‘ that’s hot/cold’. Different cells will have hot receptor proteins, or cold receptor proteins, or even receptors with different sensitivities to heat (some tuned for ‘mild heating’, others for ‘more heating’ etc).

There are also pain receptor cells, that will sense when actual damage to the skin (including from excessive heat or cold) causes release of ‘pain mediator substances’ within the skin layers. So first the cold will stimulate the cold receptors, and then the damage caused by the ‘cold burn’ will activate the pain receptors.

The cold (or more often heat) receptors are partly there to WARN you before the cold or heat is enough to cause damage – so when you touch something hot, the signal goes to your brain and your body moves your hand away, hopefully before damage (a burn) occurs.