Carrier or base oils are often applied in conjunction with an essential oil. The common industry term for carrier oils is fixed oils. These oils are made from vegetables, nuts, seeds and flowers. They are considered by many to have therapeutic properties of their own.
Carrier oils are used for several different reasons. One major reason is because pure essential oils are often too concentrated to be applied undiluted to the skin. Adding essential oils to a carrier oil also allows the oil to be spread over a larger application area and to be absorbed more evenly. Many essential oils are quite expensive, and because they are so highly concentrated, one or two drops may be all that you need. The use of a smaller quantity of essential oil is often more beneficial than a larger quantity and is certainly less likely to cause any type of reaction.
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