The Hair
Proteins, lipids, and minerals
Recent discoveries based on highly sensitive proteomics techniques show that human KIFs (Keratin Intermediate Filaments) are composed of acidic (type I) and neutral (type II) keratins organized in bundles. Each keratin forms paired structures in a twisted spiral pattern, grouping into larger structures called Protofibrils. Protofibrils, in turn, arrange themselves in groups of four to create even more reinforced structures known as Fibrils. The empty spaces within these complex configurations are filled with proteins generically known as Keratin-Associated Proteins, or KAPs.
KAPs
Keratin-associated proteins
Two groups of proteins, generically called High-Sulfur KAPs, contain a large amount of sulfur amino acids and form cross-links between keratin fibrils, serving as the main components responsible for the structural resistance of hair strands. A third group, consisting of Low-Sulfur KAPs, is known as the HGT group. KAPs from this group do not form cross-links with fibrils and act as a filling material between macrofibrils, adding flexibility and resistance to fibers.
Because they are not chemically bound to macrofibrils, HGT group KAPs are less resistant than High-Sulfur KAPs. Consequently, these proteins are the first to be damaged and removed by chemical or physical treatments on fibers, causing a decrease in cohesion between matrix proteins and leading to hair strand fragility.
Hair Fiber Structure
