The benefits of soybean oil for the skin.

Soybean oil, or Glycine Soja Oil as it is known in INCI terms, is a vegetable oil highly regarded for its moisturising properties. These properties are derived from its biochemical composition , particularly its richness in oleic acid. This omega-9 plays a key role in skin hydration as it is part of the hydrolipidic film. This is a layer composed of a water-fat mixture present on the surface of the epidermis, which helps to protect it from certain external aggressions such as wind or cold.

The moisturising virtues of soybean oil also allow it to slow down the ageing of the skin, and more specifically to prevent dehydration fine lines. These small superficial streaks tend to appear in your twenties, particularly around the eyes and lips, where the skin is thinnest. By providing good hydration to these areas, soybean oil helps to delay their onset.

Dry skin, feelings of tightness, rough touch... These issues are well known to people with dry or atopic-prone skin. Fortunately, solutions exist to restore comfort to the skin. Rich in linoleic acid, a fatty acid that contributes to the formation of the skin's waterproof barrier, soybean oil helps to nourish the skin and provides it with the lipids it needs.

Studies have indeed shown that a deficiency in linoleic acid leads to the weakening of the epidermal barrier and an increase in the transepidermal water loss (TEWL). This then increases skin dryness and irritations. Regular application of soybean oil can help to avoid these discomforts.

In addition to protecting the skin by keeping it hydrated, soybean oil has a antioxidant activity that allows it to counteract the damage caused by free radicals, which are responsible for premature skin ageing. Generated following exposure to UV rays, pollution or tobacco, these reactive molecules contribute to the alteration of protein structure, leading to skin damage (wrinkles, skin sagging, hyperpigmentation). The antioxidant properties of soybean oil come from its high content of vitamin E, a compound capable of converting hydrogen peroxide into water before it attacks cellular constituents.

Extended exposure to the sun, hormonal fluctuations, or prolonged skin inflammation are factors that can disrupt melanogenesis and trigger the onset of pigmented spots. Although harmless, this hyperpigmentation impacts the uniformity of the complexion and can be a source of discomfort or insecurity. Certain active ingredients have demonstrated depigmenting properties that are beneficial in reducing these marks.

Among these, we find soybean oil, capable ofinhibiting the activation of the PAR-2 receptor. This results in a decrease in the phagocytosis of melanosomes by keratinocytes, the cells of the stratum corneum. The transfer of melanin from the deep producing cells of the skin to the cells of the superficial layer is thus reduced, as is skin pigmentation.

It is also attributed to soybean oil a tightening effect, highly sought after in the formulation of treatments for mature skin. Indeed, studies have shown that this active ingredient stimulates the synthesis of collagen, elastin and fibrillin-1, proteins found in the connective tissue of the skin and contributing to its firmness and flexibility. In addition, soybean oil has a protective effect on elastin as it inhibits the activity of certain elastases, enzymes catalysing the hydrolysis of elastin.

Combined with its moisturising properties, these effects of the soybean oil explain why it is frequently found in creams, serums, or balms aimed at slowing down skin sagging and reducing the appearance of wrinkles.

An ally for sensitive skin, soybean oil is soothing and calming. Its anti-inflammatory properties indeed allow it toreduce redness, irritation and itching. From a biological perspective, soybean oil, and more specifically the lecithin in its composition, reduces the production of interleukin 1-β (IL-1-β) and tumour necrosis factor (TNF-α), which are pro-inflammatory cytokines. Lecithin also acts on the signalling pathway related to the nuclear factor NF-κB, which is involved in the synthesis of these cytokines.

Finally, it has been demonstrated that this compound suppresses the transcriptional activation of the gene coding for cyclooxygenase-2 (COX-2), a key enzyme in the biosynthesis of pro-inflammatory prostaglandins. Thus, soybean oil acts at various levels of inflammation to soothe and relieve the skin.

Finally, it appears that soy may have another, lesser-known property: inhibiting hair growth. Indeed, a few scientists report this effect, although the mechanism behind it is not fully understood. A study was conducted with three men who have dark beards and shave every day. For 6 weeks, they applied soy milk to half of their face immediately after shaving. By the end of the fourth week, the hair in the treated area was softer to the touch and the area appeared more sparse. A computer-assisted analysis quantified these observations. The results are compiled in the table below:

It would thus appear that soy may be a beneficial active ingredient for slowing hair growth. However, caution is advised. Indeed, although the results of this study are encouraging, it is important to note that it was based on only three volunteers. Furthermore, it was not soy oil that was used, but soy milk, which has a biochemical composition that is slightly different. If future studies are conducted using soy oil and a larger number of participants, it would be interesting to see if they arrive at the same conclusions.

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

• SHAPIRO S. & al. Soymilk reduces hair growth and hair follicle dimensions. Experimental Dermatology (2001).

• BERARDESCA E. & al. The cosmetic treatment of wrinkles. Journal of cosmetic dermatology (2004).

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

• KIM J. Y. et KIM L. Chondroprotective effect of curcumin and lecithin complex in human chondrocytes stimulated by IL-1β via an anti-inflammatory mechanism. Food Science and Biotechnology (2018).