Hair Physiology

Hair Porosity

Porosity is best defined as the hair shaft’s ability to absorb moisture. The hair shaft is relatively impermeable to water and other substances as long as there is no cuticular damage. The cuticle can become more vulnerable due to changes caused by permanent waves, coloring, as well as temperature or pH changes. The vulnerability of the cuticle permits penetration and damage to the cortex. The cuticle can be rendered permanently damaged upon repeated injury, which allows moisture to escape causing the hair to become dry and brittle leading to split ends.

Hair Elasticity

Hair Elasticity measures the tensile strength of the hair. Hair elasticity is based on having a healthy cortex. Normal hair should be able to stretch to about 1 and 1/3 its original length with enough strength to support a 100-g weight without breaking. If a hair shaft displays poor elasticity it is likely to break easily during grooming as well as product application.

Hair Texture

The thickness of the hair shaft and the feel of the hair itself are the key factors in determining hair texture. The tight adhesion of the cuticle to the cortex and the flat arrangement of the cuticular scales can cause hair texture characteristics that are associated with wiry hair. Due to the characteristics of wiry hairs, they are usually more resistant to chemical changes.

Hair Permeability

Hair Permeability is affected by the degree of porosity, elasticity, and texture of the hair shaft with the porosity and texture having the major influences on permeability. Porosity clearly plays a greater role than texture. However, fine hair will absorb more applied product than coarse hair given the same degree of porosity. Coarse hair with great porosity will still have greater permeability than fine hair with low porosity.