Yellow Clay: What are its benefits for hair?

Matifying, yellow clay is an ingredient often found in shampoos or masks intended for individuals whose hair becomes greasy quickly. This ingredient is indeed capable of absorbing excess sebum at the scalp level and ridding it of its impurities. Yellow clay thus leaves the hair light and soft. By preventing the accumulation of sebum, it also helps to combat dandruff. Studies have indeed highlighted that in some cases there is a link between an overproduction of sebum and the appearance of dandruff. This is explained by the fact that dandruff is sometimes due to the proliferation of Malassezia type fungi that feed on sebum.

Yellow clay also possesses adsorbent properties, derived from its ionic composition and crystalline structure. Indeed, yellow clay carries a negative charge at its core and a positive charge on its surface. This charge difference allows it to bind certain microorganisms to its surface for elimination. Thus, the application of a treatment enriched with yellow clay contributes to "purifying" the scalp and cleansing it.

Yellow clay is composed of several metals, some of which possess antioxidant properties. This is particularly the case with iron, which is capable of neutralising free radicals through an electron donation. These reactive species can potentially weaken the hair follicle, and promote hair loss and split ends. Therefore, the application of yellow clay to the hair has a protective effect on the hair and limits the effects of exposure to UV radiation and pollution.

Furthermore, it slows down the appearance of grey hair, which a study has shown to be correlated with the presence of free radicals. Indeed, although the mechanism by which these operate at the level of hair fibres remains poorly understood, it seems that free radicals could trigger a chain reaction leading to the degradation of melanin, the pigment that gives hair its colour.

This pertains to indirect evidence, as no study has demonstrated that yellow clay itself prevents the occurrence of split ends and white hair.

The presence of copper in yellow clay might suggest that this ingredient could have a strengthening effect on the hair bulb and hair fibre. Indeed, this metal plays a role in the synthesis of collagen, a protein that surrounds and structures the follicular units. Moreover, copper is necessary for the activity of lysyl oxidase, the enzyme catalysing the formation of aldehydes from lysines. The aldehydes produced during this reaction then assemble amongst themselves, which causes the cross-linking of collagen fibres.

Indeed, according to some studies, collagen would stimulate the synthesis of keratin, the main constituent of hair. This fibrous protein contributes to the structure and protection of hair fibres. It forms the scales of the cuticle, the outermost layer of the hair. This layer ensures the impermeability of the hair fibre and the protection of the cortex.

Let us note that once again we are dealing with indirect evidence, as the scientific studies have not been conducted on yellow clay, but on copper, antioxidants and collagen.

• CARRETERO M. Clay minerals and their beneficial effects upon human health: a review. Applied Clay Science (2002).

• SEIBERG M. Age-induced hair greying - the multiple effects of oxidative stress. International Journal of Cosmetic Science (2013).

• Thèse de François HERNOT. L’argile, son utilisation à l’officine (2016).