The Mechanical Properties of Hair II. Chemical Modifications and Pathological Hairs

The direct measurement of the ultrasonically determined modulus of elasticity (UME) has been extended to chemically modified hair and to pathological hairs. Single hairs are equilibrated at 75% relative humidity and studied with simultaneous stress-strain tests and direct measurements of the UME. Disulfide reduction with IM dithiothreitol produced more extensible hairs in which the UME retains its characteristic relationship to the stress-strain curve (i.e., initially decreasing during the Hookean zone and yield zone, and then increasing during the post-yield zone). Oxidative treatment of hairs with bleaching agents produced a different change in the UME, the UME did not exceed its initial values until late in extension. The abnormal UME was observed with a normal stress-strain curve. Hairs from individuals in one family with epidermolytie hyperkeratosis had an abnormal UME which rarely exceeded baseline levels; the UME was normal in two other families with epidermolytic hyperkeratosis. Hair from patients with hyper- and hypothyroidism, homocystinuria, female acquired diffuse hair loss, trichorrhexis nodosa, ichthyosis vulgaris, x-linked ichthyosis, and lamellar ichthyosis and normal test results. The various chemical modifications and pathological hairs are discussed in relation to current models for the mechanical properties of hair