When you purchase various vegetable oils (which are primarily cold pressed) for cooking and consuming, you will discover that over a period of time of 3-9 months, depending upon the type of oil it will begin to turn rancid and develop an off odour. Different vegetable oils vary in their shelf life. Storing vegetable oils in dark glass containers at slightly cooler temperatures (rather than in a cupboard above your stove) will help to maintain their freshness. It is recommended that some vegetable oils be kept in the refrigerator – but it is dependent upon the type.
Essential oils are primarily distilled from aromatic plant materials and typically do not go rancid in the same respect as vegetable oils. Over time essential oils will lose their freshness and crisp odour. When essential oils become oxidized they are more likely to cause dermal irritation – specifically citrus oils.
Many essential oils begin to breakdown or become oxidized when they come into contact with air (oxygen) – therefore never leave bottles opened. Specifically cold pressed citrus oils contain high levels of limonene which begins to oxidize at the very moment that it is exposed to oxygen. To extend the shelf life of a citrus oil beyond 6 months store them in the refrigerator.
Essential oils are often termed as volatile (meaning to evaporate) because they contain naturally occurring alcohols. Top note oils such as peppermint, rosemary, and eucalyptus contain high levels of alcohols so they tend to evaporate more quickly than those that contain less alcohol. Generally speaking top note oils should last 6 – 12 months (some say longer). Middle note oils such as lavender and geranium should last even longer 1 – 2 years. Base note oils such as cedarwood, patchouli and sandalwood tend to be more viscous, are darker in colour and have lower alcohol levels resulting in a longer shelf life (possibly 2 – 4 years).
Storing essential oils in dark glass containers and not exposing them to drastic temperature fluctuations and away from direct sunlight will help to preserve your oils. If you invest in a large bottle of an essential oil such as 1 – 2 oz (30-60 ml) then over time the oil should be decanted into a smaller bottle to reduce the ratio of air-to-oil in the bottle. Replacing the orifice reducer (dropper cap) periodically can also help to maintain the freshness of an essential oil.
All essential oils should be blended into a carrier oil (natural vegetable oil) in order to use them on your skin. It is the carrier oil that goes rancid (often within 3 months) – a rancid carrier oil smells like old cooking oil. In order to render your aromatic body oil concoctions from going rancid and reduce the risk of allergens (such as almond oil) consider using fractionated coconut oil.
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Note: Aromatherapy, like any other natural therapy, is intended to complement not replace traditional medicine. When in doubt about any medical condition, always seek medical advice. See legal
Sandra Topper, Professional Aromatherapist & Aromachologist