Give you heartburn. Dr. Byron Cryer is a gastroenterologist in Dallas. And he says peppermint oil has been shown to relax the muscle at the opening of your esophagus, allowing food and acid to back up, and cause that telltale burning sensation. That’s why peppermint is actually good for nausea – it quells your stomach, but that relaxed state can cause acid to creep up your esophagus.