Essential oils are natural organic materials and as such have a finite useable life span. Although they do not typically have a best before date their effectiveness can diminish over time through oxidation or bacterial breakdown.

Oxygen, heat and sunlight can attack the oils and cause their chemical structure to break down, the oils may then resinify and start to develop artifacts that detract from the oil’s odour profile and therapeutic properties. Some of these reactions may also cause allergenic constituents to arise in the oil, resulting in irritation or sensitization that can lead to skin rashes, burns, peeling skin and other undesirable side effects.

Degradation of essential oils

The three major factors responsible for essential oil degradation are:

• Atmospheric oxygen: Exposure to oxygen changes the chemical composition of the oil. This tends to occur most in essential oils rich in reactive terpenes, such as Lemon and Pine. Oxidation has detrimental effects on the aroma and therapeutic properties of the oil and can lead to increased hazards such as sensitisation. It may also affect the viscosity of some oils. Oxidation is speeded up by both heat and light.
• Heat: Essential oils are made up of a variety of constituents. The lighter constituents are the most volatile and exposure to heat can cause these to evaporate more quickly. These lighter constituents are often the ones that are gentler on the skin, so when they evaporate, leaving behind the heavier constituents, there is increased risk of the oil causing irritation.
• Light: Exposure to ultraviolet light promotes free radicals and speeds up the oxidation process. Citrus oils are particularly susceptible to light deterioration. Once oxidation has started it is difficult to stop, however it is a very slow process that can take months.

Typical shelf-life of essential oils

Each essential oil has a different rate of degradation, which is determined by its chemical constituents, and how susceptible these are to oxidation or evaporation. In general, most oils will keep well for at least 1-2 years if stored correctly. Certain essential oils, particularly top note oils (e.g. citruses), will degrade more quickly and will need extra special care and attention. These should ideally be used within 6 months.

Robert Tisserand states that refrigeration is the best single way of maximising the shelf life of your oils. You can use the following shelf-life guidelines for oils that are cared for properly and stored in the fridge. These timescales are from the point of opening the bottle and should be halved for non-refrigerated oils:

• 1 to 2 years: Angelica Root, Citrus oils, Cypress, Frankincense, Lemongrass, Neroli, Tea Tree, Pine and Spruce oils.
• 2-3 Years: virtually all other essential oils.
• 4-8 Years: Sandalwood, Vetivert, Patchouli. While the aromatic quality of these oils can actually improve and mellow with age, the therapeutic benefits can still deteriorate. If using therapeutically it may be advisable to use within the lower timeframe.

Please note these are only rough guidelines. There really are no guarantees on how long an oil will last and there can be a very wide variation in the shelf life of different oils.

How to store essential oils correctly

In order to maximise your oils' shelf life Base Formula recommends that you follow these simple guidelines:

• Buy from a reputable supplier: Ensure that you are buying 100% pure therapeutic grade essential oils. Specialist aromatherapy suppliers such as ourselves typically have a high turnover of oils which ensures a fresher purchase. We source from only the most reputable distillers and take extreme care in the storage, handling and bottling of all our oils. If you do buy from a shop, make sure the oils haven’t been sitting in direct sunlight or under hot lights. Remember it is always best to buy little and often.
• Protect against UV light: Keep your oils in either UV filtering, dark coloured glass bottles (amber coloured glass is the best at keeping out UV light) or resin lined metal containers (we use EP resin lined aluminium bottles for larger quantities of oil which are totally impervious to light).
• Protect from exposure to air: Keep your oils in the smallest possible sized bottles to reduce the amount of empty space in the container. Any empty space will be occupied by air which speeds up the rate of oxidation. It is best to rebottle your oils into smaller containers as they are used up! This reduces the ‘headspace’ i.e. the amount of oxygen in contact with the oil. When using your oils remember to replace the caps as quickly as possible and ensure that they are tightly closed.
• Store at the correct temperature: Oils must be kept in a cool, dry place, away from sources of heat. Storing your oils in the fridge is recommended and will help them last up to twice as long. To avoid the oils tainting your food keep them in a storage box or container. It should be noted that some oils can become more viscous when stored in the fridge, making them more difficult to pour. Rose Otto can completely solidify. Warming the bottle slightly in the hand before use should help.
• Avoid excessive transportation: This should be kept to a minimum as any agitation to the oil in its vessel will increase the surface area exposed to the atmosphere and therefore the oxidation process. Storing and transporting your oils in a specially designed essential oil case will help to reduce movement if you do need to take them out and about.
• Record dates: Keep a record of when you purchased your oils and when you opened them so that you’ll be more aware of when they might be approaching the end of their life.

How do you know if your oil has gone off?

If you are familiar with the characteristics of the ‘fresh’ oil it should be relatively easy to detect if an oil is past its best. If the oil appears a different colour, has a different or acidic smell, or if it looks cloudy or thick (resinous) this indicates oxidation. Once oxidised the risk of sensitisation increases and the oil is no longer safe to use for topical application.

What can you do with oxidised essential oils?

As mentioned above, oxidised oils should not be used for application to the skin. For the same reasons, they shouldn’t be used in diffusers, burners or room sprays as they could potentially irritate the mucous membranes. Old oils are however still useful for household cleaning. You can use a couple of drops as a toilet, drain or bin freshener. Pop a couple of drops on a cotton pad and place in your vacuum bag (if you have one) or mix them into household cleaning products. Remember though that the therapeutic properties (e.g. antibacterial activity) may have diminished and ensure that you avoid contact with the skin due to increased risk of sensitisation.

Please note that large quantities of ‘old’ essential oils should not be disposed of down the drain.

Base Formula sell a range of storage cases for your essential oils and aromatherapy supplies that can help you protect your oils and keep them nicely organised. Visit our website to find out more!

Sharon Lovett
Marketing Manager

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