Peppermint oil is an extract from parts of the herb, Peppermint, which has been used as a digestive aid since ancient times. Nowadays, it is used as a flavoring additive to sanitary products, such as toothpastes and mouthwashes. Menthol, a compound in peppermint oil, is also used in lotions that are applied to the body to relieve conditions such as congestion and muscle pain.