The shelf life of a particular essential oil can be difficult to calculate. The shelf life will depend on the type of oil and the grade of oil. Different qualities of oil are used for various things and they come in several grades. Aromatherapy oils for instance, are usually less pure than those used for homeopathic healing and natural health.
The purer the oil, the more likely it will be to last a long time. Essential oils that are not a high grade include oils in addition to the main oil that is comprised of animal oils and vegetable oils. These oils have a tendency to expire in as little as 6 months to one year.
Storage of the oils can also greatly affect their lifespan. If an essential oil is not stored properly in a cool, dry place in a glass container, they can become fermented. Hot temperatures can break down the materials and cold temperatures can freeze the oils.
Some oils can last for centuries. Researchers and anthropologists have cited that many Egyptian tombs still smell of essential oils from the mummification process. These oils were 100% natural and stored in a cool, dark tomb. With pure oil and proper storage, some oils can last an incredibly long time.
