Soybean Oil and Hair: What are the Benefits?

Soybean oil is valued in hair care for its moisturising properties, allowing it to make hair shiny and soft. This action of the soybean oil comes from its composition, and more specifically from its richness in saturated fatty acids, such as palmitic acid. The latter indeed contributes to the restoration and cohesion of the cuticle, the outer part of the hair fibre that ensures its impermeability and protection. When the structure of the hair fibres is solid and the scales that form the cuticle are properly linked, the hair appears more shiny, as they are better able to reflect light.

Soybean vegetable oil also has protective virtues on hair fibres. These are derived from the unsaturated fatty acids it contains, and more specifically from its oleic acid content. This naturally occurring omega-9 in the hydrolipidic film that coats the hair helps to protect the fibres from external aggressions and keep them hydrated. Therefore, soybean vegetable oil stands out as an interesting ingredient for dry or damaged hair.

Furthermore, soybean oil exerts an indirect protective effect on hair keratin, the protein that provides strength and flexibility. Indeed, as previously mentioned, the palmitic acid found in soybean oil has a chemical structure similar to that of the lipids making up the hair cuticle, allowing it to integrate and act as a intercellular cement. In doing so, it contributes to the protection of the cortex, the intermediate layer of hair fibres rich in keratin.

UV rays, pollution... These everyday factors are known to be generators of free radicals within cells. These reactive species cause several damages and are particularly likely to weaken the hair bulb and promote hair loss and the appearance of split ends. To protect against the effects of oxidative stress, it is beneficial to incorporate antioxidant treatments into your hair care routine.

Soybean oil is a good candidate as it is rich in tocopherols (vitamin E), natural antioxidants whose effectiveness has been demonstrated in several studies. If we look at their biological mechanism, tocopherols act by transforming hydrogen peroxide (H₂O₂), which is unstable and reactive, into water (H₂O). In doing so, tocopherols, and by extension, soybean oil, help to counteract oxidative stress and protect hair fibres.

Soybean oil also provides benefits to the scalp, particularly offering relief to irritated, dry, or sensitive scalps. This soothing action is due to the presence of lecithin in its biochemical composition, a molecule with anti-inflammatory properties. Indeed, several studies have highlighted that it acts on the production of interleukin 1-β (IL-1-β) and tumour necrosis factor (TNF-α), pro-inflammatory cytokines.

Lecithin also suppresses transcriptional activation of the gene encoding for cyclooxygenase-2 (COX-2), a key enzyme in the biosynthesis of pro-inflammatory prostaglandins. Furthermore, lecithin inhibits the signalling pathway associated with the nuclear factor NF-κB. This factor is involved in the production of certain pro-inflammatory cytokines, as well as interferon-gamma (IFN-γ) in T lymphocytes. IFN-γ is synthesised as part of the innate immune response and plays a role in the regulation of various inflammatory mechanisms. Thus, by acting at different levels, soybean oil soothes the scalp and can alleviate its itchiness.

The soybean oil can be used pure on the hair or be added to a hair care product. It is often incorporated into conditioners or hair masks. There are several ways to use soybean oil on the hair:

• In an oil bath along the lengths.

  Oil bathing is a technique frequently mentioned for deeply nourishing the hair. To be carried out once or twice a week, it will strengthen and restore shine to your hair. To perform an oil bath, we recommend applying strand by strand a few drops of soybean oil, from mid-lengths to ends, and leaving it on for about fifteen minutes. Be careful not to use too much oil as this could weigh down your hair. After the oil bath, you can proceed with a shampoo.

• As a mask on the scalp.

  To soothe an irritated or itchy scalp, it is possible to apply soybean oil directly to the scalp. Once again, a few drops are more than sufficient. Gently massage to allow the oil to penetrate and wait at least 30 minutes before shampooing. Do not hesitate to shampoo twice if necessary, as soybean oil has a relatively greasy nature.

• 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).

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