Can essential oils expire?

Recently, a customer wrote in with the following question:
Good day,
Purchased a couple bottles of oil from you.
Just heard oils expire. Can you tell me how long is the shelf life, as well as what happens if you use the oil after expiration date.
Also how can the life of the oil be extended.

Regards
S. M.

p.s. If one generally opens and closes a bottle of oil daily to inhale the scent, does this diminish the life of the oil and what could be done to preserve it.

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OUR RESPONSE:

Hello Mr. M.,

Yes, undiluted essential oils do have a shelf life, generally 1 year after the retail container is first opened. Some oils last 2 years or more, and others get better with age, such as patchouli oil and tea tree oil. The oils that expire the quickest are citrus oils and can be extended if kept in the refrigerator or other cool conditions.

In most cases, the best way to preserve the oils is to keep them in dark, cool locations away from light and heat. If you open the bottle daily, you might want to consider an aromatherapy inhaler. All you need to do is put a few drops of your oil in the inhaler and sniff when you desire. The inhaler scent can last several weeks depending on how much you add. This way, the oil stays in the bottle without being opened everyday, and you still can smell it anytime you want with the inhaler.

Generally, over time and oxidation, the oils become less effective. Unless the oil is contaminated in some way, there should be little harm in using them a short time after the expiration date. You may notice the aroma changes over time as well.