Essential oils will not go rancid as many carrier oils can; however, they do have a finite shelf life and will continue to degrade, lowering their healing value.
Over time, all essential oils will begin to degrade. A process in which a chemical substance changes because of external factors such as temperature, light, and oxygen are recognized to have a crucial impact on essential oil integrity.
Reasons for Essential Oil Instability
Degradation of essential oils depends on several chemical and edaphic factors that influence both the possibility of the essential oil to oxidize as well as the course of the reaction. External factors such as temperature, light, and oxygen availability are recognized to have a crucial impact on essential oil integrity.
A temperature rise of 50 degrees F approximately doubles chemical reaction rates, a relation that can be consulted to predict stability at different temperatures (Glasl 1975).
Ultraviolet (UV) light and visible (Vis) light are considered to accelerate auto-oxidation processes.
The major players for corrosion and oxidation are oxygen and atmospheric moisture. Oxidation reactions are among the leading causes for spoilage of essential oils, if not even the most frequent ones, it is evident that oxygen access plays a decisive role in essential oil stability.
“The shelf-life of essential oils can vary tremendously from one botanical to the next, from one distillation to the next, from one supplier to the next, and to the care, you give the oils.
Key factors that can directly affect the shelf life of an essential oil include the following:
Quality of the raw plant material used for distillation.
Naturally occurring chemical constituents that are present in the essential oil.
Citrus fruit oils are high in limonene, which is particularly susceptible to oxidation.
The method of distillation.
The distillation conditions, method, and process.
The quality of the botanical plant used.
Care in bottling, storage, and handling of the essential oil by the distiller and supplier.
The storage conditions of the oil once you have received it.
Because many of the factors that impact shelf life begin with the botanical planting/harvesting, distillation, and initial handling/storage of your essential oil, it is important to purchase essential oils from a supplier that you trust.
Some essential oil suppliers can share the date of distillation for each lot of essential oil they maintain. Responsible suppliers store essential oils in conditions that are far superior to what we as consumers can do. For instance, some keep their bulk oil inventory sealed, nitrogen blanketed, and refrigerated or stored in a cold room to protect the oils and dramatically reduce the risk of oxidation.
Therefore, an oil that was distilled a year ago is stored under pristine storage conditions will maintain its therapeutic integrity far better than an oil that was distilled more recently, but that was not stored well or was mishandled.” (2)
How long do essential oils keep?
Since you are most likely not to know the exact date of distillation, you can base the timing when you first open the bottle and use the following guidelines for essential oils. You will extend and double the shelf life of the essential oil if you keep it in cold storage or refrigeration.
6 months to 1 year - (1-2 years, if kept refrigerated)
Citrus fruit oils are high in limonene are prone to oxidation. As they oxidize, the percentage of pure limonene in the citrus oil decreases significantly, because it is being oxidized into other substances.
Other essential oils with a high limonene content include: neroli (Citrus aurantium amara), lemongrass (Cymbopogon martinii), frankincense (all Boswellia species; Boswellia sacra,
B. frereana, B. papyrifera, and B. serrata), tea tree (all Melaleuca species), pine (all Pinus species), fir (all Abies species) and spruce (all Picea species).
Also, those with a high level of monoterpenes; angelica root (Angelica archangelica),
bergamot (Citrus bergamia), and cypress (Cupressus sempervirens).
1 to 1.5 years - (2-3 years, if refrigerated) Includes most other essential oils.
2 to 4 years - (4-8 years, if refrigerated) sandalwood (all Santalum species), vetiver (Chrysopogon zizanioides), and patchouli (Pogostemon cablin).
Extending the shelf life of essential oils:
Refrigerate your essential oils.
Replace the top right after use.
Keep your essential oils away from direct sunlight.
If there is a lot of air space in the bottle, replace it with a smaller bottle.
Oxidization decreases the therapeutic value of the essential oil and significantly increases the risk of skin sensitization, skin rashes, and allergic reactions.
How can you tell if an essential oil has oxidized?
The process of oxidization can be slow. You may notice that the aroma of the essential oil is not as fresh as it once was. The most significant difference is when you purchase a new bottle.
Citrus oils can look cloudy.
The consistency of the oil will become thicker.
Do not rely on tester oils in stores as a guide to a new bottle of essential oil. Testers are continually being opened and exposed to the air, probably on their way to being oxidized.
Essential Oil picture; Pixabay; Free for commercial use; Retrieved October 22, 2019.
(1) Turek, Claudia, and Stintzing, Florian C.; Stability of Essential Oils: A Review
https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12006; Retrieved September 20, 2019.
(2) AromaWeb-Essential oil shelf life web article; https://www.aromaweb.com/articles/essentialoilshelflife.asp; Retrieved October 20, 2019.
(3) Tisserand Institute; Article: Lemon on the rocks: keep your essential oils cool; https://roberttisserand.com/2013/07/lemon-on-the-rockskeep-your-essential-oils-cool/; Retrieved September 20, 2019.
(4) Article: The Safety Issue in Aromatherapy; http://pharmpress.com/files/docs/aromascich07.pdf; Retrieved October 20, 2019.