African-American hair.

Its physical properties and differences relative to Caucasian hair

Scientific innovations in chemical treatments that alter the texture of African-American hair, as well as a plethora of style trends, have spurred phenomenal growth in this segment of the hair-care market throughout the past three decades.[3] The level of research & development by manufacturers in the area of product formulation has steadily elevated; yet, a great deal remains to be learned about the unique physical properties of African-American hair. Compared to the vast body of research regarding Caucasian hair, the study of African-American hair is at best limited.

A Review of Research

In published studies, J. Menkart et al,[7] Epps et al[1] and Kamath et al[6] reveal that some important research has indeed been conducted on the physical properties of highly curly hair. The efforts of these researchers and the results of their studies serve as a starting point for the further study of African-American hair. Other general observations about hair, such as those pertaining to static charge (Jachowicz[5] and C.R. Robbins[9]) and theories about moisture content, serve as a springboard for advancing the study of African-American hair.

Shape: Menkart and Wolfram[7] report that African-American hair has a physical shape resembling a twisted oval rod, whereas Caucasian hair is more cylindrical. They found evidence of this when they made elliptic comparisons of hair cross-sections. Using a formula in which the minor axis is divided by the major axis, Menkart and Wolfram determined that African-American hair has a ellipticity index of 0.56 and Caucasian hair has an index of 0.71. The tensile-strength data gathered during this research shows that the breaking stress of African-American hair (1.24 g/denier, a unit of fineness equal to the fineness of a yarn weighing 0.05g for each 450m of length or 1g for each 9000m.) is less than that of Caucasian hair (1.41 g/denier). The yield stress for African-American hair, however, is slightly higher (0.46 g/denier vs. 0.42 g/denier).

Kamath and Hornby studied the fractographic behavior of African-American hair to view both major and minor axis at low levels of extension.[6] They examined the ellipticity of hair fibers and reported ellipticity indices of 1.89 [+ or -] 0.083 and 1.0 to 1.4 for African-American and Caucasian hair, respectively. In this study, the ellipticity index was calculated by dividing the major axis by the minor axis, which is the reverse of the formula used by Menkart and Wolfram.

Combability: Epps and Wolfram[1] conducted combing comparisons between African-American and Caucasian hair using combability techniques used by Garcia and Diaz.[2] Garcia and Diaz report that African-American hair, due to its curliness, is much more difficult to comb than Caucasian hair. It was also determined that African-American hair is easier to comb wet than dry.

Using a scanning electron microscope at a magnification of about 300X, Kamath and Hornby also observed that African-American hair display frequent twists with random reversals in direction and pronounced flattening. …