Peppermint (Mentha piperita) is the second most popular essential oil in the United States. It is cooling to the skin and gives off a fresh, grassy aroma. This U.S.-sourced essential oil comes from the prominent Yakima valley in Washington state. Peppermint is believed to be native to the Mediterranean region, although the actual origin is uncertain. The crossing of its two, parent species -- mentha and peperita -- occurred in the wild. The primary constituent of peppermint essential oil is menthol. This produces an immediate physical and pronounced sensation of coolness when inhaled or applied to the skin. Peppermint blends well with lavender, rosemary, lemon eucalyptus, tea tree, lemon, and sweet orange essential oils. In addition to body and massage oils, peppermint essential oil is often used in air fresheners like air mists and diffusions. Its refreshing, energizing effects make it ideal for travelers on long trips.