If you own a refrigerator and have ever found forgotten leftovers you know that over time things spoil. Cooking or salad oils can go rancid. But what about essential oils? Should they ever smell rancid or bad? Do they spoil in time? Do they have a shelf life or do they last forever?
The short answer is no, essential oils don't spoil or go rancid. So if you've ever had an essential oil that smells rancid, chances are it wasn't 100% pure essential oil and likely diluted with carrier oil. However, essential oils can oxidize and oxidized essential oils can cause irritation to skin when diffused. And even though oxidation might not affect the color or smell of an oil it affects the oil's properties. The rate at which oils oxidize depends on their chemistry and how the oils are stored. Light, heat, and oxygen can increase the rate of oxidation. So for the best shelf life oils should be stored in dark, cool, places, and tightly capped. Oils that are rich in monoterpene or smaller unsaturated molecules tend to oxidize more rapidly than oils that contain heavier, saturated molecules. So in general d-limonene rich citrus oils tend to last only 1 or at most two year before they begin to oxidize, while thicker oils such as cedarwood or patchouli can last six to eight years. Based on oil chemistry and proper storage:
Monoterpene rich oils: last 1 to 3 years
Monoterpenol rich oils: last 3 to 5 years
Sesquiterpene rich oils: last 6 to 8 plus years
Sequiterpenol rich oils: last 6 to 8 plus years
Phenol rich oils: last 3 to 5 years
Aldehyde rich oils: last 2 years
Ketone rich oils: last 3 to 5 years
Ester rich oils: last 3 to 5 years
Ether rich oils: last 3 to 5 years
Oxide rich oils: last 2 to 3 years
Can you use an oil once it is oxidized? Often there is no detectible odor or color difference, but there is an increased risk of skin or mucus membrane irritation. If a citrus oil is more that a year or two oil it's best to use it for cleaning rather than blend it into bath or skin products. And if you use your oils on a regular basis you are likely to use them up before they oxidize.
So in summary essential oils don't exactly go bad but they can oxidize. And oxidized oils can cause irritation and are better suited to cleaning than topical application or diffusion. The bottom line if you purchase oils use them! It took a lot of plant material, time, and effort to produce the oil. Cherish and use it. If you have any other questions you'd like answered or would like to learn more about essential oils contact Tricia.