People who use adulterated or synthetic oils worry about shelf life. Some British references on aromatherapy say one should throw away their oils every six months and purchase a fresh quantity. Such advice may be valid for certain carrier blend oils, but is not valid for pure unadulterated aromatic oils that are
the products of distillation. In order to discuss shelf life, you need to distinguish between various classes of scented oils. There are four types of fragrant
oils to consider:

 

(1) True Essential Oils (distilled, pure and unadulterated).
(2) Expressed Oils (citrus oils). (Joy contains citrus oils)
(2) Absolutes (solvent extractions--neroli, jasmine, onycha)
(4) Carrier Blend Oils (essential oils in a fatty base‹such as Valor, Exodus II, Awaken, Ortho Ease, Hope, and many others).

 

The shelf lives of these four classes of aromatic oils are different. While expressed, absolute, and carrier blend oils contain large molecules along with their small aromatic ones, pure essential oils obtained entirely by distillation contain only small molecules. Large molecules tend to be less stable than small ones. Shelf life addresses the question of chemical stability. Aromatic oils
are mixtures of many compounds. If a mixture of compounds remains stable, that is, if it does not decompose or change its chemistry over a long period of time in storage, we say it has a long shelf life.

 

If you are using pure distilled therapeutic grade essential oils, as described in Chapter One of this book, then you don¹t have to worry about shelf life. Essential oils have been found in Egyptian tombs that were still aromatic and effective‹their therapeutic properties intact‹even after thousands of years. These oils were in moderately cool, dark places tightly sealed from exposure to air and the elements. That is all they required to maintain their potency. No one knows what their true shelf life may be. All we know is that it is measured in millenia, not months.

 

As for the British oils, there is a so called aromatherapy grade of oil that is actually only 1-5% essential oil dissolved in a fatty base oil. The large molecules of fatty vegetable oils are not as stable as the tiny ones that comprise essential oils. 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. We call this ³going rancid.² 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 Btitish texts that recommend pitching your oils every six months have a valid point in reference to ³aromatherapy grade² oils. A number of blends containing pure essential oils used in North America also contain some fatty oil such as olive, sesame seed, or almond. Usually, 80% or more of these blends consist of essential oils. These are not the same as the aromatherapy grade massage oils of England which are mostly fatty, but they do have a shelf life.

 

Expressed oils, absolutes, and carrier blend oils are sensitive to heat, such as in a car on a hot day. Heat accelerates any chemical reaction and if the large molecules in these oils are prone to gradual decomposition even at normal temperatures, this process will be hastened by heat. You can tell if any damage has been done to your oils by heat by testing the fragrance. If it still smells the same as when you bought it, it is still okay. If not, then damage has occurred. Exposure to heat in excess of 90-120° F can shorten the shelf life of expressed, absolute, and carrier blend oils, but does not shorten the shelf life of true essential oils. (See section on Heat at the beginning of this chapter for a more thorough discussion on the effects of temperature on oils.)

 

Absolutes, expressed oils, and oil blends that are mostly essential and only partly fatty all have a shelf life. Experience has shown that their shelf lives can be measured in years, unless the oil has been exposed to excessive heat. If you have any such oils, your nose will know if they go bad. To know if an oil blend contains an absolute, A fatty carrier oil, or an expressed oil and could, therefore, become rancid, read the label. For example, the Young Living oil blend called JOY contains no Fatty carrier oils, but has a shelf life. This is because it contains
several citrus oils, which are all expressed oils that can spoil.

 

If you want to extend the shelf life of these types of oils, refigerate them. However, if you are using such oils over periods of time less than a few months, you don¹t need to go to the trouble of storing them in your refrigerator. They will be fine if simply kept at comfortable temperatures and away from excessive heat.

 

As for pure essential oils that are the products of distillation, you don¹t have to refrigerate them. Refrigeration does not extend their shelf life. A cool environment won¹t hurt them or help them. They will last indefinitely at normal living emperatures and will remain unaffected and intact even when occassionally exposed to the heat of a hot day in a car, provided you do not open the bottle
until it has cooled down to normal temperatures. (More on this in the section on Heat earlier in this chapter.)

 

If anyone asks you about the shelf life of a pure therapeutic grade essential oil, just say, ³5000 years at least.² If they ask you about the shelf life of an oil that has been expressed, solvent extracted, or mixed with a fatty base, just say, ³It depends.²

 

NOTE: The article above is an extract from a book to be published
in January 2005 entitled: The Chemistry of Essential Oils Made SimpleThe  by David Stewart, Ph.D. The book will be 736 pages long
and its price will be $49.95.