Choosing and storing essential oils

Essential oils are an unusually easy market to be misled in. There is no legal grading system, the words used to imply quality are invented by the people selling it, and the difference between a good oil and an adulterated one is not something a nose can reliably settle.

What follows is about separating the claims that mean something from the ones that do not, and then keeping what has been bought in usable condition — which matters more than it sounds, because an old oil is not merely weaker but more likely to cause a reaction.

The claim that means nothing

"Therapeutic grade", "clinical grade", "aromatherapy grade", "pure grade" and their relatives are marketing terms. No body awards them, no standard defines them, and a company using one is certifying its own product. The same goes for a seal or badge on a website that turns out to belong to the company displaying it.

Beyond that, anything describing an oil as suitable to swallow, or as a treatment for a named condition, is a reason to buy elsewhere. A product sold with claims to treat or cure disease is making a medicinal claim, which requires a licence it almost certainly does not have.

What a label can actually tell you

• The botanical name. The single most useful thing on a bottle. "Lavender" might be Lavandula angustifolia or the hybrid Lavandula x intermedia; "chamomile" might be Roman or German, which are different oils. A supplier who omits the Latin name either does not know or would rather not say.
• The extraction method, which changes what is in the bottle — most sharply for citrus, where an expressed oil is phototoxic on skin and a distilled one is not.
• Country of origin and, ideally, a batch number, since the same species yields measurably different oil from different places and seasons.
• A GC/MS report. Gas chromatography and mass spectrometry lists what a batch contains. Suppliers who publish one per batch are showing their work; a grade name is a substitute for doing so.
• The declared allergens. Required on cosmetic labels, and on an essential oil they are mostly the oil's own constituents — linalool, limonene, citral, geraniol, eugenol. Their presence is not a defect. It is information worth having if a reaction ever happens.

Price, and what adulteration looks like

Prices should vary enormously between oils and this is the clearest signal available. Rose, jasmine, neroli and melissa are genuinely expensive because of how much flower a bottle takes; sweet orange and lemon are genuinely cheap. A shop where everything costs about the same, or where rose costs what lavender costs, is selling something other than what the label says.

Adulteration is common and mostly invisible. A costly oil can be extended with a cheaper relative, cut with a carrier oil, or topped up with a synthetic version of its main constituent, and the result still smells broadly right. This is why batch analysis is worth more than any assurance.

The practical version: buy from suppliers who specialise, publish analyses and name their botanicals, in small bottles, rather than hunting for the cheapest. There is nothing wrong with an inexpensive oil that is genuinely an inexpensive plant.

The bottle itself

Essential oils are degraded by light, heat, air and contact with plastic. So:

• Dark glass — amber or blue. Clear glass and plastic bottles are both a bad sign, since oils can dissolve some plastics and pick up what they dissolve.
• An integral dropper or orifice reducer, which controls how much comes out and limits air getting in.
• Small bottles. Oil in a half-empty bottle is oil in contact with a lot of air. Buying less, more often, keeps it in better condition — and the same logic applies more strongly to carrier oils, which go rancid.
• A dusty bottle on a shelf has been there a while. It is a rough signal and a fair one.

Storing what has been bought

Cool, dark, upright, tightly capped. A cupboard away from radiators and windows is sufficient; a bathroom windowsill is close to the worst place available, being warm, humid and bright. A fridge extends life considerably and is worth it for citrus.

Caps go back on straight away. Most of the degradation that happens to a bottle in domestic use happens through the open neck.

Rough working lives, assuming decent storage:

• Citrus oils — the shortest, often around a year. They oxidise fastest and are the ones most worth refrigerating.
• Most florals, herbs and leaves — a few years.
• Woods, roots and resins — sandalwood, patchouli, vetiver, frankincense. These keep for many years and some genuinely improve.
• Carrier oils — months rather than years, and less if cold-pressed. Rancid oil smells of old crayons.
• Hydrosols — the shortest of all. They are mostly water with no preservative, so they need refrigerating and discarding once cloudy or sour.

The reason this is a safety matter rather than a value-for-money one: oxidised oils are more sensitising than fresh ones. Old citrus and pine oils in particular are a recognised cause of allergic reactions that the same oil would not have caused when new. An oil that smells sharp or resinous compared with how it started, or that has thickened, is finished — and that is the point to throw it away rather than use it up.

Labelling anything made up at home

Anything decanted or diluted wants labelling with what is in it, at what dilution, and when it was made. This is less about tidiness than about the fact that an unlabelled bottle of diluted oil is indistinguishable from an unlabelled bottle of neat oil, and the difference matters a great deal if it ends up on skin or in a child's hands.

Storage out of reach of children and animals applies to the diluted blends as much as the bottles they came from, for the reasons set out under using essential oils safely.

See also essential oils, absolutes and hydrosols and aromatherapy.