Don't wear your self out trying to cry on demand or sweat like a maniac.  Glycerin is a safe, non toxic liquid that can be used to simulate tears, sweat and oozing wounds.  Use a dropper to simulate tears and a stipple sponge to give the appearance of sweat.  Keep out of eyes as it can cause temporary haziness.   Add a few drops to fx burns and wounds to give the look of oozing wounds and burns.  This is a thick liquid that flows slowly for an excellent fx.   This is a great addition to any makeup artist kit.  Expect 5-25 applications per ounce.