Re: What is the chemical basis for Ben Gay making your skin hot?

Ben Gay is a topical analgesic based on a principal called counter 
irritant.  That is the active ingredient (methyl salicylate)acts to provide 
a different perception than the pain which is being experienced.  Methyl 
Salicylate is a vaso-dilator.  It acts by causing the blood vessel in the 
localized area to expand, which allows more blood to flow into the area.  
Thus an increase in localized temperature is perceived.  This is not 
exothermic.  It is a physicochemical response to the drug methyl 
salicylate.  If you want a true exothermic reaction.  Try dissolving 
anhydrous magnesium sulfate (not Epson salts) in water or adding 
concentrated HCl or sulfuric acid to water.  Any of these will generate 
heat.