How to Maximize the Shelf Life of Your
The highest quality essential oils are bottled in dark glass. The reason for this is two-fold: glass is more stable than plastic and does not “breathe” the same way plastic does. Also, the darkness of the glass protects the oil from light that may chemically alter of degrade it over time.
After using an essential oil, keep the lid tightly sealed. Bottles that are improperly sealed can result in the loss of some of the lighter, lower molecular weight parts of the oil, especially the monoterpenes and sesquiterpenes. In addition, over time, oxygen in the air may react with and oxidize the essential oil.
Store essential oils away from light, especially sunlight. While the amber glass of the oil bottles does afford some protection against visible light, the darker the storage conditions, the longer your oil will last.
Store essential oils in a cool location. Excessive heat can alter the molecular structure of the oil the same way ultraviolet light can. This can lead to changes in the fragrance and therapeutic quality of the essential oil.
From the Essential Oils Integrative Medical Guide, pg. 72