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Hair comes in a bewildering variety of sizes, shapes and colors, which leads to different appearances, tactile properties and behavioral issues. This creates the desire to name or describe these various states—in large part, to aid in directing product development efforts and ultimately to help guide formulas to those with the respective hair “type.” To this end, a plethora of hair descriptors can be conceived, based on, e.g., shape, length, color, age, thickness and/or damage level.
Another descriptor commonly used is ethnicity. While this approach has been criticized in recent times, it is easy to see why it has frequently been used. Describing hair as Caucasian, Asian, African, Latino, Indian, etc., immediately conjures up specific, albeit stereotypical, images. Moreover, most will self-identify with one of these designations.
Accordingly, product developers at both small and large multinational companies are directed to develop products for a specific ethnic market. Since the U.S., Europe and Japan have historically been the largest hair care markets, Caucasian and Asian hair have received most scientific attention. In addition, the very different conformation and issues associated with African hair has made it a frequent candidate for study—and a number of papers can be found in the literature that compare and contrast the properties of hair from these three ethnicities.1-8 Today, the emergence of important new and developing markets around the world is fueling work in other hair types as well.9
This article reviews existing knowledge relating to all hair ethnicities. It also emphasizes the considerable diversity associated with hair of any ethnicity. For more on this topic, check out TRI-Princeton's Ethnic Hair Science Symposium on Sept. 24, 2019.
Size, Shape and Colo, r
The drastic variability in hair appearance and properties might instinctively suggest the presence of underlying differences in hair structure; but, generally, this does not appear to be the case. As discussed in earlier columns, all hair essentially appears to be made from the same building blocks that egress out onto the scalp in different sizes, shapes and colors.10 It has been further argued that these simple, unexciting features can explain the vast majority of all hair issues and conditions10—even though there is often a presumption that more complex explanations must exist.
By means of illustration, the historical literature describes how Asian hair possesses relatively thick dimensions. It tends to be mainly straight in conformation; is usually heavily pigmented; and individual strands are almost spherical in cross section. These characteristics cumulatively produce the distinctive visual, tactile and manageability-related properties of this hair type, while also shaping subsequent habits and practices pertaining to styling, maintenance, etc. For example, heavy conditioning treatments are commonly employed on this hair type as it can tolerate such products without adversely weighing the hair down.
The literature similarly describes the characteristic features of African hair as being highly kinky and curly in conformation; possessing considerable variability in fiber dimensions; being heavily pigmented; and exhibiting individual fibers with the highest degree of ellipticity. This highly curly conformation tends to restrict the number of styles available to the wearer, so straightening treatments—e.g., heat or chemical relaxers—have historically been popular.
This hair is already highly susceptible to breakage, and the aforementioned treatments lead to further weakening. As such, very different grooming habits and practices result—yet, this breakage phenomenon can be rationalized simply based on the shape and conformation of individual strands.10, 11 Also, it does not necessitate the more complex explanations that are sometimes offered up.
In comparison, Caucasian hair fibers generally possess lesser dimensions, with considerable variability in both color and curvature. Individual fibers exhibit a moderate degree of ellipticity.
A Highly Variable Substrate
The above descriptions represent sweeping generalities. By means of illustration, Table 1 shows the results for mean diameters of 1,300 individual fibers from each of the three described ethnicities. As per the text books, we conclude that Asian hair is thicker than African hair, which is thicker than Caucasian hair. Moreover, as a result of the high number of replicate samples (N), a relatively small standard error (i.e., standard error = standard deviation/√N) is obtained. Accordingly, the differences between the means for these hair types is calculated to be statistically significant.
However, rarely mentioned in the text books is breadth of these distributions.
- Menkart, J., Wolfram, L. J., and Mao, I. (1966). Caucasian hair, Negro hair and wool: Similarities and Differences. J Cosmet Sci, 17, 769-787.
- Syed, A. N., Kuhajda, A., Ayoub, H., Ahmad, K., and Frank, E. M. (1995). African American hair: Its physical properties and differences relative to Caucasian hair. Cosm & Toil, 110, 39-48.
- Kameth, Y., Hornby, S. and Weigmann, H. D. (1984). Mechanical and fractographic behavior of Negroid hair. J Cosmet Sci, 35, 21-43.
- Keis, K., Ramaprasad, K. R., and Kameth, K. (2004). Studies of light scattering from ethnic hair fibers. J Cosmet Sci, 55, 49-63.
- Steggarda, M., and Seibert, H. (1941). Size and shape of head hair from six racial groups. J Heredity, 32, 315-318.
- Wolfram, L. J. (2003). Human hair: A unique physiochemical composite. J Am Acad Derm, 48(6), S106-S115.
- Vermall, D. G. (1961). A study of the size and shape of cross sections of hair from four races of men. Am J Phys Anthrpol, 19, 345-350.
- Franbourg, A., Hallegot, P., Batlenneck, F., Toutain, C., and Leroy, F. (2003). Current research on ethnic hair. J Am Acad Derm, 48(6), S115-S119.
- Aslan, S., Evans, T. A., Wares, J., Norwood, K., Idelcaid, Y. and Velkov, D. (2019). Physical characterization of the hair of Mexican women. Intl J Cos Sci, 41(1), 36-45.
- Evans, T. A. (2016). The perplexing topic of hair type. Cosm & Toil, 131(9), 24-31.
- Evans, T. A. (2017). New ideas and thoughts on hair breakage. Cosm & Toil, 132(8), 46-53.