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Composition biochimique huile de soja.

What is soybean oil composed of?

Soybean oil is a vegetable oil frequently used in cosmetics for skin and hair care due to its numerous properties: antioxidant, anti-inflammatory, moisturising... These properties stem from its natural components. But what exactly are these components? What do they contribute to the skin and hair? Here's everything you need to know about the active ingredients of soybean vegetable oil.

Summary
Published January 31, 2024, by Pauline, Head of Scientific Communication — 7 min read

What active ingredients make up soybean oil?

Soy is a legume that has been traditionally cultivated in Asia for centuries. Its seeds contain a valuable vegetable oil obtained through cold pressing. The soy oil is used in the formulation of numerous cosmetic products due to the benefits it provides to the skin and hair. Its various properties stem from its biochemical composition rich in beneficial active ingredients.

Soybean oil contains polyunsaturated fatty acids.

Soybean vegetable oil is rich in linoleic acid, comprising approximately 50 to 60% of its content. Linoleic acid is an unsaturated fatty acid, classified as essential because it cannot be synthesised by the body. This omega-6 has several benefits for the skin, particularly contributing to the formation of the skin barrier by triggering a cascade of biochemical reactions that ultimately lead to the stimulation of cellular renewal.

Linoleic acid is also involved in the mechanism of acylceramide synthesis. These are a specific type of ceramide resulting from an amidation reaction between a sphingoid base and linoleic acid. Ceramides play a significant role in the protection and hydration of the skin. These lipids, naturally present in the epidermis, indeed ensure good cohesion between the cells of the stratum corneum.

Thus, by providing the skin with the fatty acids it needs, soybean oil helps to strengthen the epidermal barrier and limit insensible water loss (IWL). This also helps to reduce the appearance of dehydration fine lines, these superficial folds that form especially when the skin is no longer able to retain sufficient water.

Soybean oil is rich in monounsaturated fatty acids.

Between 10 and 15% of soybean oil is composed of monounsaturated fatty acids, specifically of oleic acid. This fatty acid, which belongs to the omega-9 family, is naturally present in the skin's hydrolipidic film, the mantle made up of water and fat found on the surface of the epidermis. The hydrolipidic film plays a protective role that is crucial for the skin, helping it withstand external aggressions such as wind, cold, or pollution.

Soybean oil contains saturated fatty acids.

Soybean vegetable oil also contains saturated fatty acids such as palmitic acid and stearic acid, making up about 10% of its composition. These molecules have a chemical structure quite similar to that of the compounds in the stratum corneum, allowing them to easily integrate and aid in its restoration. Moreover, these saturated fatty acids have a film-forming effect on the skin, meaning they contribute to the maintenance of the hydrolipidic film.

Note : the various fatty acids mentioned are the source of the nourishing properties of soybean oil. This oil strengthens the lipid profile of the skin, a property sought after in the development of treatments for dry or atopic skin.

Soybean oil, an extract containing tocopherols (vitamin E).

Tocopherols (Vitamin E) are natural antioxidants that protect skin cells from oxidative stress. This vitamin is found in soybean oil, where it is present at about 0.01%. This percentage may seem low, but studies have shown that the tocopherols in soybean oil contribute to its resistance to oxidation and limit its rancidity over time.

From a mechanistic perspective, tocopherols act by transforming hydrogen peroxide (H₂O₂), which causes damage to DNA and proteins, into water (H₂O). This property of soybean oil allows it to care for mature skin and particularly to prevent the appearance of wrinkles, fine lines and other signs of skin sagging.

Soybean oil contains lecithin.

Lecithin is a phosphorous lipid found in soybean vegetable oil. This active ingredient has properties similar to those of fatty acids due to its closely related chemical structure. Indeed, lecithin has moisturising and protective effects on the epidermis. This active ingredient is particularly capable of integrating within the lipids of the stratum corneum to contribute to their cohesion and thus strengthen the skin barrier.

Note : It is not uncommon to find lecithin in moisturising cosmetic treatments aimed at delaying skin sagging. This active ingredient from soybean oil is quite popular and, according to some sources, may stimulate collagen synthesis by fibroblasts. However, at present, the scientific evidence is still insufficient to definitively attribute this property to lecithin.

Soybean oil contains phytoestrogens.

Finally, we find in soybean oil isoflavones, molecules belonging to the family of phytoestrogens. These compounds have the unique characteristic of causing oestrogenic or anti-oestrogenic effects due to the similarity of their molecular structure with oestradiol, a steroid hormone in the human body.

Many scientific studies have been conducted on the effect of phytoestrogens, but the conclusions vary significantly from one study to another. For some scientists, phytoestrogens represent safe alternatives to hormonal therapies and could help prevent certain cancers and neurodegenerative diseases. For others, these molecules may increase the risk of breast cancer and disrupt fertility.

With regards to soybean oil, its isoflavone content is minimal, rendering its oestrogenic power virtually nil. During the cold pressing of soybeans, phytoestrogens tend to remain in the beans and do not pass into the oil. However, depending on the quality of the ingredients used and the type of extraction, it is technically not impossible for traces of isoflavones to be present in soybean oil. At present, the effects of phytoestrogens in topical application are still being debated by the scientific community, which is why, by principle of caution, it is advised for individuals with hormone-dependent diseases to be cautious and seek medical advice when using soybean vegetable oil.

Sources

  • BONDI A. & al. Isoflavones de Soja. Caractérisation, détermination et activité antifongique. Journal de chimie agricole et alimentaire (1974).

  • BUCK D. Antioxidants in soybean oil.Journal of the American Oil Chemists' Society(1981).

  • HARRATH A. H. & al. Phytoestrogens and their effects. European Journal of Pharmacology (2014).

  • MURTAZA G. & al. Dermatological and cosmeceutical benefits of Glycine max (soybean) and its active components.Acta Polonia Pharmaceutica(2015).

  • ERGONUL P. G. & al. Cold pressed soybean oil. Elsevier eBooks (2020).

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