Coarse hair and dullness is often the result of damage to the cuticle and the loss of the protective lipid film, leading to increased roughness and uneven light reflection. On the surface of the cuticle – the outer layer consisting of flattened, scale-like cells – lies a thin, hydrophobic lipid layer, the F-layer, rich in methylicosanoic acid (18-MEA) and other lipids. If the scales become misaligned, the surface becomes irregular and porous, scattering light in all directions and increasing the rough texture to the touch (1).
Mechanical handling
Aggressive brushing, dry detangling, tight hairstyles, or even rubbing against a towel, pillow or clothing tend to tear or disarrange the cuticle scales, creating micro-irregularities, raised edges and areas of small depressions.
Excessive heat
Regular use of a straightener, curling tongs or a very hot hairdryer quickly dehydrates the hair fibre, which can denature the keratin, promote cuticle erosion and make the hair more brittle.
Chemical treatments
hair colouring, bleaching, perms and chemical straightening alter disulphide bonds and impair the cohesion of the cuticles, thereby promoting porosity and roughness (2).
Oxidative stress and photo-ageing
Sources of oxidative stress (UV, pollution, tobacco) tend to reduce the surface lipid film (F-layer), thereby exposing the cuticles to hydrophilicity, swelling and friction between the hair fibres, leading to a loss of shine and a rougher texture. UV rays degrade keratin proteins, lipids and pigments (melanin) on the surface, resulting in a stiffer, more brittle cuticle with detached scales, and a loss of colour and shine (1, 2). Pollutants, metals and smoke, meanwhile, generate reactive oxygen species which oxidise the lipids and proteins in the hair and the scalp. Furthermore, environmental factors such as hard, chlorinated water or a dry climate can increase surface dehydration and the build-up of particles, which exacerbates the dull appearance and rough texture. Finally, local inflammation or an imbalance in the microbiome can oxidise lipids and disrupt the keratinisation process taking place in the scalp, resulting in a cuticle that is already weakened as it emerges from the follicle. (1, 2, 3, 4).
