Pure essential oils do not go bad. However, these products can oxidize and deteriorate to the point that they are no longer as effective in terms of therapeutic or aromatic use. How long the life of the oil is depends on the kind of plant it is derived from. It can also be affected by the kind of process that was used in order to make the extraction and how the oils were stored.
As a guide, essential oils are at the peak of their quality for at least one year from the date that they were purchased. Provided, that the oil was bought from a reputable source that maintains a fresh inventory that is replenished regularly. The shelf life of the aromatherapy oils and products can be lengthened by keeping the products in dark glass bottles with tight lids. The best place to keep the bottles is in a cool, dry place that is away from direct sunlight.
As the oil is used up, re-bottle it into smaller bottles to keep it fresh longer. The reason for this is that the smaller bottles reduce the amount of oxygen that comes in contact with the oil, making it retain its qualities for a lengthier period of time. However, this should especially be applied to oils that are citrus or coniferous in nature. In these cases, the essential oils have terpenes, a form of hydrocarbon, and thus oxidize faster. On the other hand, thicker oils such as patchouli or sandalwood tend to become better with age. Thus, these can keep for longer and can be purchased in large amounts.
Some suppliers list the shelf life of their products to provide a guide on how long they can keep. Though these are not always accurate, they can be quite useful especially since manufacturers have a clearer idea on how the oils were distilled and the processes they went through. As a result, they are in the best position to say when the essential oils become less effective.
Buyers have the responsibility to take note of the condition of the oils before they are used for any purpose. For example, if the smell of the oil has changed drastically or has dulled, then it could be indicative that it is no longer in the best condition. Other signs that the essential oils should be disposed of is when the viscosity has changed by becoming thicker or the liquid has become cloudy.
Learning to work with essential oils as you create perfumes is a wonderful experience. Your interaction with them will enable you to, almost with a sixth
sense, determine when they have changed in nature. Be patient as you begin your relationship with them, they will teach you much.
Life Never Smelled So Sweet!