An essential oil is that aromatic, volatile liquid that is within many shrubs, trees, roots, bushes, and seeds and that is usually extracted through steam distillation. Essential oils are highly concentrated and far more potent than dried herbs because of the distillation process that makes them so concentrated. It requires a large volume of plant material to produce small amounts of a distilled essential oil. For example, it takes 5,000 pounds of rose petals to produce one kilogram of rose oil.
Essential oils are different from vegetable oils such as corn oil, peanut oil, or olive oil. Vegetable oils are greasy and may clog pores. They also oxidize and become rancid over time and have no antibacterial properties. However, most essential oils do not go rancid and are powerful antimicrobials. Essential oils that are high in plant waxes, such as patchouli, vetiver, and sandalwood, if not distilled properly, could go rancid over time, particularly if exposed to heat for an extended period of time.