Remember BenGay? There was a time when the cool, tingly ointment was the only way to quickly relieve the tenderness associated with sore muscles. But BenGay is completely synthetic — check out Skin Deep's breakdown of the salve's toxicity. Though methyl salicylate, the chief ingredient in the BenGay, is naturally found in Sweet Birch (a.k.a. Black Birch) and wintergreen, massive manufacturer Pfizer still synthesizes it.