Pure essential oils are made up of complex chemical compounds that give each oil its therapeutic properties and characteristics. Unlike poor quality aromatic oils, essential oils are made without the use of additives or carrier oils. That makes them susceptible to instability in its composition, causing the essential oil to lose its therapeutic effects as time goes by.
What causes essential oils to change?
If truth be told, essential oils do not "expire". This is attributed to the fact that they do not contain water and is mainly made up of chemical compounds from plant derivatives (bark, flower, fruits, stem, etc). But what is true is that environmental factors can change the chemical composition of essential oil, degrading the quality of the essential oil as a result. This is normally where one would say that the essential oil has "expired" or "gone rancid".
So what are the three environmental factors that are responsible for changing the chemical makeup of essential oils?
1. Oxygen
From the time a fresh new batch of essential oil is produced, farmers take extreme measures not to expose the oil to oxygen. This is because oxygen is a chemical element itself and when introduced to the essential oils, it starts changing the DNA of the oil, which in turn, hastens the degradation of the essential oil. Of course, when you open a bottle of essential oil, you cannot prevent oxygen from contaminating your oil, but with an orifice reducer, it restricts the inflow of oxygen into the bottle, slowing down the oxidation process.
2. Heat
You might have seen the phrase "keep away from heat/sunlight" on the packaging of your essential oil box before, but how many of you have actually taken this information seriously to actually keep your essential oils in a proper place? When you feel that the smell of your essential oil isn't as potent as the first time you sniffed it, then the culprit is most likely the heat evaporating the volatile constituents in your essential oil and making your essential oil smell lighter than before.
3. Light
Ultraviolet light promotes the formation of free radicals. When an essential oil is exposed in UV light, the chemicals in the oil starts to change. Some chemicals may increase, and some may decrease. These changes will affect the potency and scent characteristics of the essential oil. To prevent UV light from affecting the essential oil, amber glass bottles are used to store essential oils instead of the clear glass. The dark glass will protect the essential content from the harmful UV light.
How Do I Know If My Essential Oil Has Gone Bad?
One key characteristic of essential oil that has gone bad is the potency of the smell. As essential oil deteriorates over time, the intensity of the oil gets weaker and weaker until it loses its potency. When that happens, its therapeutic effects that accompany it are also out the window. Some oils may start to smell sour and rancid, and that is a clear indication that it's time to get a new bottle.
Other essential oils may have visible changes in its appearance, depending on the viscosity (thickness) or the colour of the oil. If you have placed your essential oil out in the sun for too long, it may cause some essential oils, especially absolutes, to solidify. Exposing your essential oil to oxygen will also oxidise your essential oil, changing its colour from a clear liquid to a yellow tint. Do bear in mind that different essential oils will have different colour naturally, so it is best to monitor your own essential oil's colour rather than comparing it with a different essential oil.
How long can my essential oil last?
There is no fixed shelf life of essential oils since the rate of deterioration depends on how well the oil is being kept, but here is a rough guide on some of the common chemical compounds found in essential oils and how long it roughly takes for each to go bad.
- Sesquiterpenes: 8 to 10 years
- Cedarwood
- Ylang Ylang
- Patchouli
- Myrrh
- Sesquiterpenols: 10 to 15 years
- Sandalwood
- Monoterpenes: 2 to 3 years
- Lemon
- Orange
- Grapefruit
- Frankincense
- Bergamot
- Monoterpenols: 5 to 6 years
- Tea Tree
- Peppermint
- Palmarosa
- Rose Absolute
- Lavender
- Geranium
- Esters: 5 to 7 years
- Roman Chamomile
- Helichrysum
- Jasmine Absolute
- Aldhydes: 4 to 5 years
- Lemongrass
- Ketones: 5 to 7 years
- Spike Lavender
- Clary Sage
- Oxides: 3 to 5 years
- Rosemary
- Eucalyptus