Other Approaches for Evaluating Stretching Properties of Hair

Korastoff [61] has shown that human hair from patients with hypothyroidism and acromegaly show a characteristic alteration in the yield region of the stress/strain curve (at low humidity) compared to hair from control groups. Swanbeck et al. [62] have shown that patients suffering from congenital ectodermal dysplasia have hair of low tensUe strength. 

Monilethrix is a genetic anomaly in which hair fibers contain periodic constrictions along the fiber axis. Monilethrix hairs tend to fracture at these constrictions [63] and therefore must exhibit abnormal stretching behavior. Trichorrhexis nodosa is another abnormal condition, where hair fibers contain nodes at irregular intervals along the fiber axis. These nodes actually contain tiny fractures and tend to form broom like breaks [63] under stress. Therefore, nodosa hair fibers should also exhibit abnormal stretching behavior. Other hair shaft anomalies such as trichothiodystrophy and Menkes syndrome should also display abnormal stretching behavior consistent with the abnormal hair shaft condition associated with these diseases. 

Other Approaches for Evaluating Stretching Properties of Hair 

Several other approaches have been used for studying the stretching properties of human hair. Among these approaches are vibrational methods [10, 11], stress relaxation [46], stretch rotation [65], set and supercontraction [19], fatiguing [66], and extension cycling [67]. 

In this scheme, a fiber is attached to a beam with a known natural resonant frequency. Tension (within the Hookean region) is applied to the fiber. The beam is then deflected. From the change in the oscillation frequency of the 

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Other Approaches for Evaluating Stretching Properties of Hair 403 Physiological Abnormalities... 

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