Wintergreen (Gaultheria procumbens) leaves and oil contain methyl salicylate, a compound similar to aspirin. When rubbed on the skin, it creates a warming sensation and helps dampen pain signals.
You'll find wintergreen oil in liniments, creams, and balms made for sore muscles, joint discomfort, and arthritis. Apply it only to the skin. Swallowing even a small amount can cause serious poisoning.