How to Store Essential Oils to Keep Them Fresh

Keep essential oils in their dark glass bottles, caps screwed tight, in a cool cupboard away from sunlight, heat and children. That covers most of it. The rest is knowing which oils age fastest, how to tell when a bottle has turned, and how to look after oil once it's sitting in a diffuser reservoir.

The four things that age an oil

An essential oil is a mix of small, volatile aroma molecules, and many of them react slowly with oxygen. Chemists call this autoxidation. Four things speed it up:

• Light. UV light drives oxidation. Amber or dark glass blocks most of it, so keep oils in their original bottles and out of sunny spots.
• Heat. Warmth speeds up every reaction and makes the lighter top notes evaporate faster. Room temperature in a closed cupboard is ideal. Windowsills, shelves above radiators and bathrooms are not.
• Air. Every time a bottle is opened, fresh oxygen gets in. Close it straight away, and remember that a nearly empty bottle holds more air than oil.
• Time. Even a perfectly stored oil changes eventually. Freshness is something you use up.

Which oils age fastest

Not every oil keeps for the same length of time. As a rough guide, from quickest to slowest:

• Citrus peel oils such as lemon, Brazilian Sweet Orange, Italian Bergamot, South African Grapefruit and Gannan Aged Mandarin Peel. They're rich in limonene, which oxidizes readily. Open them when you plan to use them, and use them first.
• Herb and leaf oils such as Moroccan Rosemary and Australian Tea Tree. They sit in the middle.
• Flower oils such as Provence Lavender and South African Geranium. These keep reasonably well.
• Wood and resin oils such as Virginia Cedarwood and Indian Oud. Heavier molecules make these the slowest to change.

How long Zhithera oils keep

Unopened, Zhithera's essential oils and fragrance oils have a shelf life of three years from the production date on the label, provided they stay sealed, cool and out of the light. Once a bottle is opened, or the oil is poured into a reservoir, it's best used up fairly soon. A sensible rule of thumb is within a few months for citrus oils and within a year or so for most others. That isn't an expiry date. It's when the scent is most likely to still smell the way it did the day you opened it.

Writing the opening date on the label takes two seconds and saves guessing later.

How to tell an oil has turned

• The scent smells sharp, sour, flat or a little like turpentine next to how you remember it.
• The oil looks cloudier or darker, or feels thicker than it used to.
• It mists less freely than before. Older, thicker oil leaves more residue on a diffuser mesh.

If an oil has clearly changed, replace it rather than trying to mask it with a stronger setting.

Looking after oil in a diffuser reservoir

The 6.5 mL reservoir shared by the Zhithera D1 and D1 mini closes with a silicone plug, which keeps air out between sessions.

• Day to day, leaving oil in the reservoir is fine. Keep the plug seated and wipe away any spills on the outside.
• If you won't use it for a while, take the reservoir out of the diffuser, wipe it, keep the plug in and store it upright somewhere cool and dark. Wipe the diffuser body dry as well; oil left sitting on the body or charging contacts can mark them.
• In the car, don't leave a reservoir in a vehicle parked in strong sun. A closed car heats up far beyond room temperature, which is hard on both the oil and the electronics. Refill and swap reservoirs only when the car is safely parked.
• Treat the plug gently. Don't pull or stretch it. If it tears, the seal is no longer complete. Keep that reservoir upright at home or replace it, and don't use it in the car or carry it in a bag.
• One oil per fill. Topping up an old oil with a new one blurs both scents. Finish it, wipe the reservoir, then refill.

The reservoir itself doesn't expire. Its mesh is a reusable part that wears with use, so it's worth considering a fresh refillable cartridge after about five refills, or sooner if the mist weakens. A spare also makes it easy to switch scents without wasting what's left in the first one.

A simple storage routine

1. Keep all oils together in one closed cupboard or box, away from heat and out of reach of children and pets.
2. Store bottles upright with caps tight.
3. Date each bottle when you open it, and use citrus oils first.
4. Keep oils away from open flames and heaters; concentrated oils are flammable.
5. Give the diffuser mesh a gentle wipe now and then (how to clean and maintain your diffuser).

Frequently Asked Questions

How long does an unopened bottle of Zhithera oil last?

Three years from the production date on the label, as long as it stays sealed, cool and out of the light.

Should I keep essential oils in the fridge?

There's no need; a cool, dark cupboard works well. If you do refrigerate oils, let the bottle reach room temperature before opening it so moisture doesn't condense inside.

Can I leave oil in the diffuser reservoir?

Yes, day to day, with the plug in place. If you won't be using it for a while, take the reservoir out, wipe it and store it upright somewhere cool.

Why do citrus oils go off faster?

They're high in limonene, which reacts with oxygen more readily than the heavier molecules in wood and resin oils. Open citrus oils when you plan to use them, and use them up first.

Essential oils and fragrance oils are aromatic products for diffusion only and are not intended to diagnose, treat, cure or prevent any condition. Do not apply them to skin or swallow them, and keep them out of reach of children and pets.