Oxygen, Essential Oils Worst Friend

In the world of Essential Oils, a key question is do essential oils expire? We first must understand what is expiration and best before.

Expiration vs Best Before

Expiration dates and best-before dates are important considerations when it comes to essential oils. Expiration dates refer to the date after which the oil is no longer safe to use, whereas best-before dates indicate that the oil is still safe to use, but the quality may not be as good after the specified date.

Generally, essential oils should not be used after their expiration date. This is because over time, essential oils naturally degrade, and using them beyond their expiration date may lead to undesired results.

On the other hand, best-before dates are simply an indication that the oil’s quality may not be as good after this point. This doesn’t mean that the oil is unsafe to use, and some users may still find it to be of acceptable quality.

It is likely a best-before date takes into account packaging stability. This includes the micro leaking of oxygen into the packaging, evaporation of volatile compounds and the evaporation of water.

What’s is oxidation and rancidity?

Oxidation and rancidity are two common forms of deterioration that can occur in essential oils. Oxidation occurs when oxygen molecules come into contact with certain compounds in the oil, leading to oxidation reactions and the formation of free radicals. This can cause a change in the original aroma of the oil and impaired therapeutic benefits. Rancidity, on the other hand, is a form of decomposition caused by the growth of certain bacteria and fungi. This can cause the oil to develop an unpleasant smell and taste.

The term rancidity is related to oxidation.

Do all Essential Oils Oxidize?


Due to the nature of essential oils containing numerous compounds, it is likely other compounds will oxidize as well.

What are Oils?

Essential oils are highly concentrated plant extracts obtained from flowers, leaves, roots, stems, seeds, bark, and other parts of plants. Each oil has its own unique aroma and properties, such as antiseptic, anti-inflammatory, anti-depressant, analgesic, antiviral, and so on. Essential oils are used in aromatherapy, massage, and other natural remedies to improve mood, reduce stress, and support overall well-being. They are also used in cosmetics, perfumes, and food flavoring.

What is Oxygen?

Oxygen is a colorless, odorless, tasteless gas that makes up roughly 21% of the air we breathe. It is essential for all living organisms and is produced by plants through the process of photosynthesis. Oxygen is a vital element in many metabolic reactions, and is necessary for cellular respiration. It is found in the atmosphere, in water, and in the cells of all living things.

Why is Oxygen an Oils Worst Enemy?

Oxygen is oils worst enemy because it can cause oxidation, which in turn can break down the oil’s molecular structure and reduce its effectiveness. Oxidation can also create sludge that can clog up engine components, leading to decreased performance and expensive repairs. Additionally, oxygen can react with certain components in oil, such as antioxidants, reducing their efficacy. Finally, oxygen can cause oil to become acidified, leading to corrosion and further damage to the engine.

Are Oxidized Rancid oils harmful?


Rancid oils are harmful because they contain a form of oxidation that is not beneficial to human health. They contain free radicals, which can damage cells and contribute to chronic diseases, such as cancer and heart disease. Rancid oils also contain degradation products, including aldehydes, ketones, and lipid peroxides, which can cause gastrointestinal, hepatic, and neurological problems. Additionally, rancid oils may contain potentially toxic compounds, such as trans fatty acids, which can increase the risk of chronic diseases (1). Furthermore, the taste and smell of rancid oils can become unpleasant, making them less enjoyable to consume.


1. B. E. Bowen, F. D. Gunstone, J. L. Harwood, and F. Padley, Eds., The Lipid Handbook, 3rd ed., CRC Press, 2009.

How do I identify or test the oil being Rancid?

Test for Oxidation Rancidity of Oil at Home.

The simplest test to conduct at home is the smell and taste test (using food-grade oil). If the oil doesn’t have the familiar aroma or emits a repulsive, rancid odor reminiscent of spoiled cooking oil, it is likely rancid

Chemically Test to Determine the peroxide value.

The peroxide value of an oil can be determined through a chemical process. This process involves the oxidation of organic compounds in the oil. The oxidation reaction is accelerated by the presence of traces of peroxide in the oil. The amount of peroxide present can be measured and calculated to determine the peroxide value.

To begin the process, a sample of the oil is taken and diluted with an organic solvent such as dimethylformamide (DMF). A few drops of an accelerated oxidation reagent, such as potassium persulfate, is then added to the oil sample. This reagent reacts with the organic compounds in the sample, increasing the oxidation activity.

At this point, a known amount of thiocyanate is added to the sample. This allows the release of hydrogen peroxide generated from the oxidation reaction to be measured. The amount of hydrogen peroxide is determined through a reaction with ferrous ammonium sulfate, which produces a red color. This color is then measured and used to calculate the peroxide value.

The final step involves calculating the peroxide value using a formula based on the amount of hydrogen peroxide released in the reaction. By following these steps, the peroxide value of an oil can be accurately determined.


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