Using essential oils is a natural way to scent your candle. Unlike fragrance oils, these scents do not contain any artificial additives but are made from 100% natural ingredients. Does this also mean they can expire?

Can they expire?

Essential oils do not expire in the traditional sense, i.e. they do not become rancid, mouldy or fungal like food. However, over time, they undergo a process called oxidation, which changes the oil's perceived scent, sometimes viscosity, and after a certain period of time they lose their therapeutic effect and may become ineffective in applications such as aromatherapy and scenting candles. It is important to note that oxidized essential oils can cause skin irritation and when inhaled they can trigger a cough. It is therefore important to discuss the shelf life of essential oils.

The good news is that going bad is a very slow process. For most essential oils it takes several years before the oxidation process starts. So, if you use essential oils within 12 months of purchase, in most cases this issue will not even arise.

How can I tell if my essential oil has "gone bad"?

Oxidation changes the chemical composition of essential oils, which leads to changes in their properties, including changes in aroma, colour and viscosity.

What are the main characteristics that can be used to determine whether an essential oil has deteriorated?

• Colour: It will change colour, becoming darker, lighter or even colourless depending on the oil.

• Oil appearance: Very old essential oils can become more viscous and eventually solidify, but this usually takes several years.

• Scent: The aroma changes slightly, depending on the oil, becoming stronger and more unpleasant, or weakening and possibly losing its freshness. Although you may only notice this when you compare it to a new, fresh oil. Smell the essential oil before use to notice the change in scent. This is obviously easier for those who use them more often.

How to preserve and maximize the life of essential oils?

If you want your favourite oil to last longer in the bottle, there are steps you can take to ensure this.

Proper storage of essential oils simply means keeping them in dark bottles, in a cool, dark place out of sunlight, with a cap on when not in use. The less time you expose them to oxygen, the longer they will last. Given that most essential oils are flammable, keep them away from open flames and other heat sources, including candles, gas stoves, fireplaces and matches.