The main part of a hair primarily consists of natural polymers: 90% of a hair’s dry weight compromises proteins (α-keratin). Keratins are rich in cysteine, an amino acid that is characterised by its sulphur content, which contributes to hair’s characteristic insolubility and resistance to enzymatic degradation
The thiol groups of two cysteine residues can form a covalent bond of several polypeptide chains. And, as such, any change in the cysteine content leads to a change in the hair’s flexibility. The physical properties of human hair are largely determined by the water absorption capacity of its cellular components. This depends on the ratio of hydrophilic to hydrophobic amino acid residues and the degree of protein cross-linking. Under normal conditions, human hair has a water content of 10%, which significantly influences its mechanical properties.
Conventionally, hair care products targeted keratin or moisture content, but lipids are an important constituent of hair too. They represent 1% -9% of the total mass of hair and play an eminent role in its physiochemical characteristics. For instance, they are essential in giving hair its mechanical strength. The cuticle cells are covered with a thin lipid layer, which is covalently bound to the hair keratin. The internal lipids are situated between the lipid layer and consist of approx. 60% free fatty acids.
During the process of hair ageing, lipids are gradually lost from the hair. Moreover UVA/UVB and even visible light take part in the destruction of lipids in hair which suffers like our skin from photo-ageing. Up to 40% of all free fatty acids are destroyed during the hair’s ageing process.
Log in or register FREE to read the rest
This story is Premium Content and is only available to registered users. Please log in at the top of the page to view the full text.
If you don't already have an account, please register with us completely free of charge.
