You've done your homework and identified a quality source of essential oils. The company provides gas chromatographic proof that the oil is as pure as it can get, the oils are provided in high-quality dark glass bottles, and your aromatherapy is working well. However, while cleaning out your fridge a thought suddenly occurs: What is the shelf life of essential oils?
They Break Down
Yes, essential oils will go bad. The shelf life of essential oils isn't something anyone can predict with accuracy, unlike say lettuce that predictably turns into goo after a week or so. That is because the shelf life of essential oils depends entirely on how and where they are stored. Bacteria and mold will not grow in essential oils, but their chemical structure can and will break down after exposure to:
Shelf Life of Essential Oils is Affected by Storage Conditions
Storing essential oils in a cool place, such as in the refrigerator, will significantly prolong their shelf life. Keeping them next to the oven or on top of a radiator is really not recommended. Admittedly, some oils will become very viscous or even turn into a solid if kept in a refrigerator, but simply letting them sit out for a few hours before use will solve that problem.
Most manufacturers sell their essential oils in dark glass bottles to help protect them from light, but it's a good idea to place the bottle inside another light-proof container for storage. One study showed that exposing essential oils to light for just an hour caused significant degradation of their chemical structure.
Air Affects the Shelf Life of Essential Oils
Oxygen is the key environmental factor that is practically impossible to keep away from your essential oils. Obviously, oxygen is found in the air and it makes its way into the bottles of essential oil every time they are opened. The oxygen that gets inside the bottle then gets mixed with the oil as you move the bottle around or re-insert the dropper. Oxygen will react with the essential oils and degrade their chemical structure.
The shelf life of essential oils being regularly exposed to oxygen varies from oil to oil, but in general if the bottle is being opened for use on a daily basis it should be assumed around 60% of the oil will have broken down into other chemicals after a year. If the oil is only used once a month or so, it will have a longer and more unpredictable shelf life.
Only Buy What You Will Use
We recommend carefully considering how much of a particular essential oil you will use and try to only purchase a year's supply at a time. If you want the purest essential oils, their shelf life should be assumed to be only a year. Most likely they have a shelf life that is longer than that, but why take the chance?