Apparent fragility of African hair is unrelated to the cystine-rich protein distribution: a cytochemical electron microscopic study.

A feature of black African hair is an apparent increased fragility of the hair shaft compared to other ethnic groups (as measured by the tensile force needed to break the hair fibre). This has certain similarities to that reported for trichorrhexis nodosa (weathering secondary to physical damage) and trichothiodystrophy [a genetic disorder associated with reduced cystine (sulphur)-rich proteins and increased fragility]. In the present study, the distribution of the cystine-rich proteins in the hair of black Africans was compared to that of Caucasian and Asian volunteers, plus patients with trichorrhexis nodosa and trichothiodystrophy, using transmission electron microscopy and specific silver stains. It was found that the silver staining pattern of the hair shafts of black Africans was similar to that observed for Caucasians, Asians and also patients with trichorrhexis nodosa. The cuticular cells exhibited an electron dense A layer and exocuticle, and in the cortex the microfibrils forming the macrofibres were outlined by electron-dense material. This contrasts with the abnormal distribution of the cystine-rich proteins seen in trichothiodystrophy. This study is the first formal comparison of the cystine-rich proteins in the various racial groups and shows that there is no abnormality in their distribution in black African hair shafts compared to the other ethnic groups. Therefore, the excessive structural damage observed in the African hair shafts is consistent with physical trauma (resulting from grooming) rather than an inherent weakness due to any structural abnormality.