Can hair really be hydrated?

As a reminder, each hair fiber has three stacked layers: the medulla, the innermost layer; the cortex, which accounts for nearly 80% of the fiber; and the cuticle, the external protective layer. The cortex consists of keratin and also contains melanin pigments that give hair its color. It also serves as the primary site for water storage and absorption. The cuticle consists of flat cells that overlap like shingles, and their cohesion is essential for limiting water loss. When these cells become disorganized, often after damage to the lipid intercellular cement, the hair fibers become more porous: they retain less water and absorb it more easily.

Hair cannot be hydrated in the strict sense because it is biologically inert. Its water content can be maintained.

Hydrating hair does not mean simply wetting it in the shower. Water itself penetrates little into hair fibers and evaporates. The true challenge of hydration is to support water retention in the cortex while protecting the cuticle to prevent loss. To achieve this, use conditioners or masks that contain humectant agents, capable of attracting and retaining water within hair fibers. Common humectants include glycerin, hyaluronic acid, and urea. These hygroscopic molecules bind water around themselves and ease its absorption into the cortex when the cuticle is more permeable for a short time, such as immediately after shampooing.

To keep water in the hair, restore the cuticle’s lipid barrier. Emollients and occlusive agents act here. Plant oils, like coconut oil or apricot oil, rich in fatty acids, can form a film on the fiber surface, reducing water evaporation. Some studies have shown that lauric acid, a primary component of coconut oil, can penetrate hair, reduce cuticle swelling from water, and lessen the stress this swelling places on hair fibers.

Some studies examined the effect of nanoemulsions on the hydration of textured hair from a woman. Some hair fibers underwent a bleaching process with or without recoloring. For reference, a nanoemulsion is a mixture of two or more immiscible liquids in which one liquid disperses in the other as nanometer-scale droplets. Three nanoemulsions were studied: a control formulation, one containing 7.5% coconut oil, and one containing 7.5% coconut oil and 0.1% wine lees extract. They were applied to all three hair types and hydration was measured.