The characteristics of vegetable oils useful in cosmetics

Understand your cosmetic products, for a reasonable and sensible use. In order to choose and use vegetable oils in your cosmetic routine, it is important to have several notions in mind. Because we always choose better when we know what criteria we are relying on, The company of the senses offers you a small overview of the questions to ask yourself before choosing a vegetable oil in cosmetics!

Related articles [View] - The Guide of the vegetable oils in aromatherapy, natural cosmetics and nutrition - Precautions for the use of vegetable oils - How to check the quality of a vegetable oil? - Really take care of your hair with vegetable oils - What are vegetable oils made of? - Which vegetable oil for my skin? - The 50 most used vegetable oils in aromatherapy, nutrition and cosmetics

The comedogenicity of vegetable oils

An oil is saidto be comedogenic if it leads to the formation of comedones. Comedones are all the small imperfections that one can have on the skin such as pimples, microcysts or even blackheads. They appear when the skin produces excess sebum that ends up clogging the pores. Combination to oily skin and especially young skin, are generally the most prone to blackheads that will be found at the sebaceous glands.

A comedogenic oil is therefore an oil that will promote the formation of these imperfections and therefore clog pores in the long run. Nevertheless, these oils can very well be used from time to time and especially on dry skins, to solve a specific problem like wrinkles, stretch marks or simply to rehydrate the skin.

Each oil has a comedogenicity index that depends on 3 criteria: its freshness, its sensitivity to oxidation and its speed of penetration into the skin. The comedogenicity index of an oil varies from 0 to 5, with 0 being non-comedogenic and 5 being highly comedogenic. While these indices indicate the likelihood of an oil being comedogenic, it is equally important to consider your skin type and therefore possible unexpected reactions. Oily to combination skin types will therefore be advised oils with a low index between 0 and 2, while normal to dry skin types will be able to more easily use oils with indices between 0 and 5.

More details:

The oxidation of vegetable oils

Vegetable oils are often defined by their oxidative potential, this is a degradation of the fatty acids that make up the oil and which will therefore alter the quality of the oil. This oxidation can be caused by various factors such as oxygen in the air, light, interactions with the container or even heat. Oxidation of an oil can thus increase its comedogenic index and lead to allergic reactions and the appearance of imperfections in addition to a rancid odor upon use.

More details on: the oxidation of vegetable oils.

A dry or fatty vegetable oil?

When applying a vegetable oil to the skin, it is possible to feel a greasy sensation, while the oil no longer penetrates the skin as well. This phenomenon is due to the fatty acid composition of the oil, which gives it a more or less strong affinity with the skin. The more affinity the oil has with the skin, the faster it will penetrate and the less greasy you will feel to the touch. These are the penetrating, plant-based oils that are called dry oils. Dry oils will be primarily composed of omega 3 and omega 6 which penetrate the skin more easily, while fatty oils will be more composed of omega 9. The choice of vegetable oil will therefore depend on your needs, if you want to keep a matte skin, without feeling greasy, you need a dry oil. If your goal is to give your skin a satin finish, a fatty oil will be just right.

Here are some examples of vegetable oils with a dry or greasy feel:

Virgin or refined oil?

The virgin oil of first cold pressure refers to the method of obtaining the oil, which differs from that of refined oils.

A virgin oil is obtained by cold pressing, which is a simple, fast and ancient method of extraction. It is a mechanical extraction method, where the oleaginous fruits and seeds are pressed, to extract the oil directly. This mechanism is done at room temperature so as not to denature the fatty acids. A virgin oil from first cold pressing is therefore the first juice of the seed or fruit, without chemical treatment or refining. This is a gentle extraction method that preserves the oil in its entirety, for a product rich in vitamins, antioxidants and other unsaponifiables.

In contrast, a refined oil is obtained by an extraction method, using a solvent, often alcohol. Once this oil is obtained, it undergoes several treatments:

  • A demucilagination which corresponds to the elimination of phospholipids in the oil, complexes grouping one or more fatty acids to other molecules;
  • A neutralization, to make the oil lose its free acidity;
  • Discoloration and deodorization.

All these steps often require the intervention of chemical molecules. This implies the destruction of certain essential fatty acids if the refining temperature is high, as well as the loss of the natural composition of the oil. Also, new components can be created, not necessarily beneficial for the skin or for food. Refined vegetable oils have the advantage of being better preserved than virgin vegetable oil.

Be careful when you choose an oil, if the method of obtaining is not specified, it is certainly refined!

What is the saponification number?

The saponification index (SI) is a value used in the process of saponifying a fat. There are two saponification numbers, the one for potash (KOH) and the one for soda (NaOH). In chemistry, the saponification number corresponds to the mass of potash or soda in mg required to neutralize the free fatty acids and saponify the esterified fatty acids contained in 1g of fat.

In other words, the saponification number of an oil is the quantity in milligrams of potash or soda needed to saponify 1 gram of that oil. Each vegetable oil has its own saponification index, indeed depending on the oil used the amount of potash or soda will be different. This index thus allows to characterize the oils.

Saponification is therefore a chemical reaction between a fatty substance (vegetable oil or butter) and a base such as potash (KOH) or soda (NaOH). There are two types of saponification, hot and cold saponification. Cold saponification is often preferred, since it retains all the goodness of the oils and therefore results in a better quality soap.

This method is widely used in cosmetics and particularly for the manufacturing of soaps. Indeed, the saponification number is an important data to know the necessary amount of strong base to add to saponify a vegetable oil or a butter. Generally, soaps made with soda will be hard, while those made with potash will be softer or even liquid.