It is much like any other muscle rub but nongreasy. The menthol in the solution causes skin irritation~heat~ and the alcohol evaporating causes a cooling sensation. The sensation of these two feelings keeps one from feeling the underlying muscle or bone pain for awhile.
When used with an oral analgesic, the Biofreeze can override the pain symptom long enough for the oral med to kick in, or can override the pain sensation long enough so that one can move stiff muscles and loosen stiff joints without experiencing pain during the process.
ETA: Family Dollar has a cheaper version that works as good and as long for about $1.65 a jar.
When I was in high school I was putting IcyHot on my calves after a run, and the tube exploded. I was in underwear and it got on my thigh. HOLY HECK! I'm so glad it didn't get higher, because it burned like crazy! Your poor doctor probably forgot to wash his hands *before* going to the bathroom. BioFreeze is pretty strong stuff.
I use BioFreeze to help me get to sleep in the summer if my back is acting up. I can't stand a heating pad if the house is warm, and it works just as well. There is a generic brand in drugstores here called Max Freeze. I don't like the texture as much, but it works well.