What is the difference between essential oils (volatile oils) and carrier oils (fixed oils)?

Essential oils are also known as volatile or ethereal oils. They are not technically an oil, but a hydrophobic liquid that evaporates. Some of the main chemical ingredients in essential oils is alcohols, aldehydes, esters, ethers, ketones, phenols, and terpenes. Essential oils are only obtained through the distillation, hydro-distillation, or vacuum distillation of various aromatic parts of a botanical, including the leaves, bark, stem, or flowers. The color of essential oils ranges from clear to yellow, and are highly concentrated. They have a very strong aroma of the plant they were obtained from. The oils are used by volatizing or diffusing in carrier oils, diffused into the air, or burned as an incense. Due to their potency, some people may have allergic reactions to essential oils, particularly if used undiluted on the skin. Essential oils do not go rancid, but can oxidize and lose their beneficial properties over time. Carrier oils are a true oil, and are also known as fixed oils, vegetable oils, or based oils. However, not all carrier oils are vegetable oils, as they can be derived from animals in very rare cases. Examples include coconut, olive, argan, and jojoba oils. The oils are taken from the fatty portion of a plant, seed, nut, or animal, through a variety of methods including supercritical extraction, cold-press, solvent extraction, maceration, and centrifuge. Some of the main components of carrier oils are lipids, such as fatty acids, waxes, and fat-soluble vitamins like vitamin A, D, E, and K. Most lack a strong aroma. Carrier oils do not evaporate, but tend to stay “fixed” on the skin, giving them the often-used name of fixed oils. The name “carrier” oil comes from their use as a carrier for essential oils into the skin. Because essential oils are so potent, they need to be diluted before they can be applied directly to the skin. Carrier oils do have benefits on their own, such as nourishing, healing, softening, anti-aging, and protective properties. Unlike essential oils, carrier oils will eventually go rancid with time.