If you live in the West, you probably pop a couple of Tylenol or Advil pills when you have an ache or pain. For other pains, perhaps you might put a thermal patch on your back or a sore joint, or use ice to combat swelling.
That is not always the case here in Cambodia, as I recently learned after finally deciding to find out about the patches that I have observed occasionally on men, women and children here.
You probably are smarter than me and thus already have figured out the reason for the patches. What they do is apply cooling gel on top of afflicted area.