Sweet birch oil is almost pure methyl salicylate, the same as wintergreen, from a completely unrelated tree. The salicylate risks are identical: it passes through skin, thins the blood, and can poison at high doses.^[2] But the bigger problem is that you almost certainly cannot buy it. A survey of 27 commercial samples sold as sweet birch found not one contained the four natural markers that distinguish real bark distillate.^[1] Every sample was synthetic methyl salicylate or wintergreen sold under another name.^[1]