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Why is it important to know the degree of oxidation of an oil or vegetable butter?

Oils are basically composed of diglycerides and triglycerides of fatty acids. Each oil has different properties depending on its composition and we can combine them to get the best out of each of them.

Thus, for example, castor oil, which alone has a low absorption capacity, combined with other more absorbent oils brings interesting fatty acids to our skin and a great capacity for hydration.

Likewise, if we want to make natural soaps, it is important to bear in mind that some oils, although they provide a good level of foam and have a great cleaning capacity, such as coconut oil; tend to dry out the skin in a daily use.

However, the combination of coconut oil with olive oil, which has a greater emollient capacity and a low rancidity index, provides us with a natural soap with greater washing and skin protection qualities.

A generic distinction is usually made between hard oils and soft oils:

-Hard oils, are those in which saturated fatty acids predominate and usually remain in a solid state at room temperature (20ºC). When heated, they melt and turn into a liquid state. Most butters are considered hard oils.

-Soft oils have a predominance of unsaturated fatty acids and remain in a liquid state at room temperature. In addition, soft oils tend to be more vulnerable to rancidity, which is the ability of oils to react with oxygen and other elements, causing them to deteriorate and smell bad. That is why it is advisable to keep in mind its expiration date.

Depending on the type of skin our cosmetic product is aimed at, we can select one oil or another. For example, oils high in palmitic acid may be interesting for the formulation of cosmetics for dry skin. Oils high in oleic acid, such as olive oil or almond oil, may interest us to improve the penetration of other assets of our formulation.

The iodine index can also help us in this decision, as oils with a higher iodine index will have an increased risk of oxidation. Thus, for example, the low iodine index of baobab oil, makes it very resistant to oxidation, and therefore very resistant to rancidity.

As we said, over time the oils become rancid due to oxidation. Unsaturated soft oils (sunflower, corn) oxidize more easily than saturated oils or butters (such as coconut, palm …) The more unsaturated an oil is, the greater the probability of oxidation. Oils high in polyunsaturated fats, Omega 3 and Omega 6, are very sensitive to heat, light and oxygen. When exposed to these elements for too long, the fatty acids in the oil oxidize and turn rancid.

Certain factors accelerate the oxidation process (oxygen, light, contact with oxidizing metals such as iron and copper, etc.) and also heat, which accelerates chemical reactions. On the contrary, other factors slow down oxidation, such as the contribution or natural richness of the oil in vitamin E. That is why oils naturally rich in vitamin E such as wheat germ oil are used in combination with other oils to protect them from oxidation.

Or vitamin E supplements, in the form of drops or capsules, are added to our formulations in order to protect them from oxidation.

On the other hand, there are oils or substances that are very resistant to oxidation and that do not need us to add any vitamins. This is the case, as we mentioned, of wheat germ oil.

Or, also, castor oil, which is more like a vegetable lanolin than a conventional oil.

The same happens with jojoba oil, which also looks more like a very fine wax than an oil and whose resistance to oxidation is also well known. Or baobab oil, which we mentioned earlier, whose low iodine value makes it very resistant to oxidation.

As we said, depending on the cosmetic formulation that we want to make and the type of skin to which it is directed, we can consider using some oils or others.

Since these oils oxidize less, they are also preserved better and for longer and, therefore, they can be very useful in the preparation of creams and products for sensitive and reactive skin with low tolerance to added preservatives.

Substances such as natural beeswax, which we can add when emulsifying our oils and natural soaps, also protect them to a certain extent from oxidation and extend their useful life.

And resins, such as rosin (colophony), which we can include in the formulation of our soaps, also prevent rancidity. Benzoin resin, for example, not only prevents rancidity, but is also used as a preservative in natural cosmetic formulations.

In an upcoming entry we will explain the procedure for making a natural preservative from benzoin balsamic resin.

Other natural ingredients that can act as antioxidants in our cosmetic preparations are: beta-carotenes, including vitamin C, astaxanthin (a very powerful antioxidant of plant origin), alum salts, which, like benzoin, would act as antioxidants and as preservatives at the same time, the Co2 extract of rosemary (oleoresin), the ESP (extract of grapefruit seeds), as well as the addition of essential oils and natural alcohols such as ethanol.

It is therefore important to keep all this in mind when formulating our products, since those that contain these ingredients, to a greater or lesser extent, may not require the addition of other types of antioxidants or more aggressive preservatives.



As we have been commenting, the oxidative potential of a vegetable oil depends above all on the type of fatty acids that compose it, so that the oils can be more or less sensitive to oxidation depending on the composition of their fatty acids and, without a doubt, according to also its process of obtaining and its conditions of conservation since vegetable oils are very sensitive to heat and temperature.

Thus, for example, cold-pressed virgin oils not only have greater emollient properties and capacities, but also tend to become less rancid. The same occurs with oils stored in glass containers and away from sources of light and heat. A good idea is to keep them in the fridge and take them out a few hours before we are going to use them.

Among the oils that are not very sensitive to oxidation, we have those of: castor oil, jojoba, baobab, wheat germ, olive, flax, apricot, almonds, avocado, hazelnut, coconut, cocoa butter, shea butter …

Among the oils moderately sensitive to oxidation, we have those of: argan, borage, grape seeds, chia, perilla, sesame…

Some oils are, however, very sensitive to oxidation, such as: sunflower, corn or rosehip …

If unfortunately, any of our oils becomes rancid before we use it, remember that it is not necessary to throw it away as it can always be used to make soap. In the soap it is not noticeable if the oil has become a little rancid, besides, the addition of essential oils and aromas will finish correcting the mess.

Talking about the oxidation of oils forces us to talk about antioxidants, which are the substances that prevent oxidation, as we have been saying.

Antioxidants are molecules capable of protecting cells from the harmful effect of external factors such as free radicals, which are highly reactive molecules capable of unleashing a very harmful chain reaction on our body, as it causes damage to many cells.

Just as antioxidants are important in the internal processes of our body, they are also important and necessary in the care of our skin, which is the largest organ we have and that fulfills numerous functions: Like the regulation of our body temperature, the balance of the passage of water both inside and outside our body, elimination of external factors that are harmful protecting the body from negative effects such as pollution or solar radiation, among others.

One of the best alternatives to meet these goals is the use of natural antioxidants in our cosmetic formulations, able to help us counteract important damages such as skin aging.


The most recent research indicates that those antioxidants that are essential nutrients for our body are also the most effective antioxidants. Among them, vitamin E, vitamin C and flavonoids.

As we always say, it is better to use the very rich oils and natural compounds that the natural oil or substance contains, than to add vitamin capsules or other types of laboratory preparations, synthetic to a greater or lesser extent.

Thus, it is possible, as we said, to add wheat germ oil to our preparations to avoid rancidity and to also provide anti-aging properties. And, likewise, it is possible to add the very rich raspberry seed oils, which contain high levels of vitamins A and E, or a grape seed oil, with high levels of polyphenols and vitamins E and K, or even avocado, which it is rich in vitamins A, D and E …

Resveratrol is widely known for its antioxidant properties that enhance collagen fibers. It provides firmness to the skin and delays the appearance of wrinkles. In addition, it has other anti-inflammatory and sun protection properties. Among its components are polyphenols, powerful active ingredients with great antioxidant properties that help fight free radicals and slow down premature aging. Oils rich in resveratrol and polyphenols would be those of grape seeds, as we mentioned before, and açai oil.

And it is also always possible to complement our preparation with green tea, mallow, oat or pomegranate plant extracts, which have a large number of natural antioxidants.

Retinol, for its part, is an active derived from vitamin A with the ability to reach the deepest layers of the skin, thus stimulating collagen and elastin. Thanks to its properties, it greatly improves the external appearance of the skin. Organic rosehip and aloe vera oils contain large amounts of natural retinol.

Recently, oligomeric proanthocyanins, which are one of the most abundant polyphenolic substances in the plant kingdom, have been added to this list. These polyphenols can be found in fruits like apples, pears, and grapes, and also in foods like chocolate and beverages like red wine and tea.

A study presented at the Society for Free Radical Biology and Medicine in Indianapolis, United States, has shown that the antioxidant capacity of oligomeric proanthocyanins can protect blood vessels from aging that is associated with a decrease in cell damage, which suggests that these substances have an anti-aging effect because they protect DNA.

Thus, it is possible to obtain this antioxidant reinforcement of proanthocyanins by adding, for example, dragon’s blood to our preparations. Dragon’s blood is a substance used for millennia for its important medicinal, anti-inflammatory, healing and disinfectant properties. It acts as a powerful antioxidant with a rejuvenating effect that acts both in the superficial layers of the skin and in the deeper layers. The high dose of proanthocyanins found in dragon’s blood helps maintain the natural collagen fibers and greatly reduces wrinkles, which are the most visible expression of tissue deterioration.


-Vitamin E (tocopherol), either in the form of drops, or in the form of gelatin capsules to take from which we can puncture and pour the vitamin E into our product; It is usually the most used antioxidant when it comes to preserving the oils and fats that our creams, soaps, and other home-made products contain. It is a powerful antioxidant that also helps the skin defend itself against free radicals and protect itself from UV rays. It also stimulates circulation, improves skin elasticity, helps prevent wrinkles, improves healing, and helps heal sores. Dosage to delay rancidity: 0.1% -0.2% of the total weight of the oils in the formula (4-8 drops per 100 g of oil).

-Astaxanthin: It is one of the largest antioxidants in the world, so the capture of free radicals is its strength. It is ten times more powerful than vitamin C, fourteen times more powerful than vitamin E, and fifty-four times more powerful than any other beta-carotene. Salmon, an animal that needs (literally) all its energy to swim for days and days against the current, has a high concentration of this component in its muscles. In fact, that is why it has that pinkish-reddish color that we all know.

Coming from a marine microalga, called haematococcus pluvialis, astaxanthin is a natural substance that provides the skin with micronutrients and manages to prevent, slow down and even improve the effects of photoaging, such as spots, small wrinkles, flaccidity (elastosis) and spider veins. Astaxanthin is a fantastic antiaging, as it reduces wrinkles and improves the elasticity of the skin. On the other hand, it minimizes the damage that free radicals can cause in the dermis and improves blood flow in the area where it is applied. Also noteworthy is the anti-inflammatory power of this compound, as well as its ability to prevent premature aging by protecting the skin from harmful UVA radiation.

In natural cosmetics it is interesting to use it (by pouring a capsule of the substance astaxanthin) in cosmetic preparations especially aimed at blurring facial blemishes and protecting us from solar radiation.

If you have this possibility, you can add it to your sunscreen formulations, since it acts as a powerful natural biological filter, and also in anti-blemish and anti-aging cream formulations.



However, it is a cumulative pigment whose overdose can cause yellowing of the skin. It is therefore important not to exceed a small capsule in our cosmetic preparations. Likewise, if we decide to ingest it to protect ourselves from solar radiation, it is important that we do not take more than the prescribed dose.

-The Co2 extract of rosemary (oleoresin). The antioxidant properties of this extract are mainly due to the presence of carnosinic acid, which can help stabilize mixtures of oils and products that contain oils. It also has anti-inflammatory effects on the skin and can help fight free radicals (a good choice for ‘anti-aging’ soaps). Dosage: 0.1 – 0.4% of the total weight of the oils (2-8 drops per 100 g of oil).

-Benzoin resin, which, as we have said,not only prevents rancidity, but is also used as a preservative in natural cosmetic formulations. Dosage: 0.5- 1% of the total weight of the oils.

-Wheat germ oil: It is an oil with a high content of vitamin E, which transfers great preservative properties to the products to which it is added.

-Other frequently used antioxidants are: Grapefruit seed extract* (GSE* Grapefruit seed extract is a powerful antioxidant thanks to its high content of vitamin C and flavonoids), essential oils (all of them have antioxidant capacities to a greater or lesser extent), Vitamin A, Vitamin C (ascorbic acid), beta-carotene, etc …


If you liked this article, leave us your comments 🙂



  1. Lorraine Magarian

    I’ve already been using organic castor oil in glass with an expiration of 2025. Is it still good even if the bottle has been opened or is the date applicable if the bottle is unopened?

    • Castor oil can turn rancid, definitely! I wouldn’t use it further than the indicated date. And it’s best to avoid storing it in warm environments, in UV exposed locations or where moisture can get into it.
      This oil becomes much darker in colour when it oxidises going from a light yellow to a darker yellow and onto a slight orange tone, and that’s a good way to know if it is too late to use it!

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