by mac standards this is not allowed. even tho you santitize your hands, mac doesn't allow you to place product on your hands. i don't understand it, but that's company policy. the only product i can imagine you would want to warm up would be the paint pots. to soften them up, place the petri dish in your hands (both sanitized of course) and allow the heat from your hands to warm the glass. then place the paint pot product on the dish and work from there.

why you can't use your hands when:
they are sanitized
you touch there face applying shadows (lifting saggy lid skin)
you move their head for better angles

i don't know. but, i've seen some of the artists doing that. i have caught myself doing it here or there.