A Keratin Fiber Sheath

In 1968, researchers discovered that when hair fibers were treated with hot ethylene glycol, a fiber-like residue remained that appeared to be a continuous sheath around the hair, which was resistant to acid and alkalis but dissolved with hypochlorite treatment. This residue differed from the epicuticle, which is resistant to hypochlorite. Upon acid hydrolysis, 30% of the residue's weight was recovered as amino acids, with a composition different from that of whole hair, suggesting that the sheath may not be entirely proteinaceous. The study indicated that the sheath could be a previously unrecognized structure associated with hair fibers.