14 November 2008

Carrier oils can go rancid (oxidizing) over time. How quick an oil becomes rancid is affected by the level contain of natural fatty acids, tocopherol (Vitamin E), method of extraction and the characteristic of the oils it self. However, this process usually takes up to a year and these products should have been used long before such a long period.

Fatty oils also contain proteins, polypeptides, and amino acids,unstable compounds not found in essential oils. Fatty oils will naturally break down into smaller molecules over time at normal room temperatures. It’s the sign that the oil going rancid.

While large molecules have no smell, the smaller molecules resulting from the decomposition of fatty hydrocarbons do have a smell, an unpleasant one. Hence, an aromatherapy grade oil that is mostly vegatable oil does have a shelf life. Thus, the British texts that recommend pitching your oils every six months have a valid point in reference to “aromatherapy grade” oils.

If you come across a carrier oil that has a strong, bitter aroma, the carrier oil may have gone rancid. If you can, compare the aroma of the oil that you suspect is rancid with the same botanical oil that you know is fresh.

Carrier oils that you purchase should be natural and unadulterated. Exceptions include buying carrier oils that have natural vitamin E added. Vitamin E acts as a natural preservative.
When purchasing carrier oils, estimate the quantity of oil that you think you'll use within the lifetime of the oil. It’s very good to buy smaller sizes of these products more regularly, rather than the one purchase of a larger size. If you are not going to use the oil quickly it can be a false economy.

See the Carrier Oil Shelf life for more information.

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