The new study, carried out by cosmetics firm Kao and Gifu University in Japan aimed to explain the age-dependent change of cuticle and its effect on hair properties by evaluating hair fibres collected from Japanese females.
It found the hair cuticle becomes more fragile and the hair surface properties deteriorate in the same age range as the age-dependent changes on density and elasticity (40-50), which has been previously studied.
“Once the cuticle receives extensional stress, the fine-structure, which is broken first, is the cell membrane complex (cmc) between cuticle cells in the young ages, while it shifts to inner endocuticle in the elder ages,” say the study authors.
“The transition period is around the 40s. Embrittlement of endocuticle leads to cuticle loss through daily grooming more directly than that of cmc. A rugged residue tends to be exposed at the hair surface and 18-MEA levels are reduced in elder ages.”
Testing
In this study, researchers collected hair fibres from Japanese females, ranging from 10 to 70 years old, and evaluated them in the aspects of inclination for each type of damage, resistance of cuticle against grooming stresses and content of fatty acid 18-MEA on hair surface.
The results showed that the dominant damage pattern shifts from where the cell membrane complex, the structure located between cuticle cells, is split and the cuticle lifts up (type L), to where the fragile substructure of the cuticle cell (endocuticle) is damaged so that its rugged residue is exposed (type E), with ageing.
Furthermore, the cuticle becomes gradually less resistant to daily grooming stress. The dominance of type E damage accelerates cuticle loss. Reduction of 18-MEA on weathered hair is accelerated with ageing on elder hair.
Hair structure
In our daily lives our hair is exposed to various stresses and is then gradually lost as we age, and this typically relates to patterns of type L and E cuticle damage.
Healthy human hair is covered by around seven layers of cuticle cells and these have a regular formation and hydrophobic surface; they provide hair with good texture, alignment and appearance.
The surface cuticle structure receives stresses first and thus is prone to damage.
Each cuticle cell consists of fine substructures: the A-layer, exocuticle and endocuticle. Among these, the endocuticle is the most fragile substructure due to its lower content of disulfide bonds. Between neighbouring cuticle cells, the cell membrane complex (cmc) exists.
To maintain a healthy hair surface, it is known that the fatty acid 18-MEA plays an important role, as it is covalently bound to the cuticle surface and provides lubrication, smooth alignment and contributes to the fine lustre of hair fibres.
The study was published in the Journal of Cosmetics Dermatology.