The Mentha Arvensis peppermint has hairy leaves with serrated edges and purple spiked flowers. This Japanese peppermint is known for its high menthol content so high in fact that menthol crystals sometimes form right on the leaves. Disclaimer: Please note that the international federation of Aromatherapists does not recommend that essential oils carrier oils or hydrosols be taken internally unless under the supervision of a medical doctor who is also qualified in clinical aromatherapy. Safety: Peppermint essential oil should be used well diluted since high concentration can cause a burning sensation and sensitization. Avoid use during pregnancy.