Shape Variability and Classification of Human Hair: A Worldwide Approach
From: Human Biology Date: June 1, 2007 Author: Garcel, Anne-Lise; Langaney, André; Loussouarn, Geneviève; Porter, Crystal; Saint-Léger, Didier; de la Mettrie, Roland | Copyright information Copyright Wayne State University Press Jun 2007. Provided by ProQuest LLC.
Abstract
Human hair has been commonly classified according to three conventional ethnic human subgroups, that is, African, Asian, and European. Such broad classification hardly accounts for the high complexity of human biological diversity, resulting from both multiple and past or recent mixed origins. The research reported here is intended to develop a more factual and scientific approach based on physical features of human hair. The aim of the study is dual: (1) to define hair types according to specific shape criteria through objective and simple measurements taken on hairs from 1,442 subjects from 18 different countries and (2) to define such hair types without referring to human ethnicity.
We chose to use four hair characteristics. Two of the characteristics are related to hair curliness: (1) curve diameter (CD), that is, the smallest curve diameter of hair cut at a given stretched length, referred to as L^sub 2^; and (2) curl index (i), that is, the ratio of the stretched length (L^sub 2^) to the greatest length (L^sub 1^) occupied by the same piece of hair at rest (no stress applied). The other two characteristics are related to the kinking of hair (Hrdy 1973): (3) number of twists or kinks (i), that is, a sudden constriction and twisting of the hair shaft along its main axis, expressed as number of coils per hair sample; and (4) number of waves (w) per hair sample.
Materials and Methods
Hair Samples. Hair was sampled from 1,442 human volunteers (72% women, 28% men) from 18 different countries. The volunteers were recruited at random through newspaper ads in large cities (Table 1). They were informed about both the purpose and conditions of the study and gave written informed consent.
Natural, colored, bleached, and nonchemically straightened hairs (e.g., use of styling products or heat tongs) were included because they had not been involved in a process that had permanently altered hair morphology. However, hair treated with a permanent waving or a hair straightening product within the preceding nine months was not included.
Curl Index (i). Hair is cut at a fully extended length of 6 cm from its root. This length is referred to as the L^sub 2^ value. The hair is immersed for 3 min in 100 ml of a 1% solution (in water) of a basic nonconditioning shampoo and then thoroughly rinsed using tap water and placed on a paper towel. The hair is carefully blotted. After allowing the hair to air dry, the hair is placed for a minimum of 5 min on a dry paper towel.
The hair is then carefully laid on a glass plate without applying any mechanical stress, in order to allow it to maintain its natural shape. A second glass plate is gently placed onto the hair, carefully avoiding any side shifting or sliding. The distance between the two farthest points of the hair is then measured and referred to as L^sub 1^. The curl index i is defined as the ratio L^sub 2^/L^sub 1^.
Curve Diameter (CD). When hair is placed between the two glass slides, the radius of the curvature of each hair curve can be determined by superimposing a transparent template made up of circles of known radius (expressedin centimeters; see Figure 1) and matching the curvature of the hair with the closest circle of the template. The smallest or the tightest curvature is selected as the value of the curve diameter (CD).
Number of Wave s (w). The upper glass plate is removed and the two ends of the hair fiber are taped on the bottom glass plate. Each tape must cover only 0.5 cm of hair, with the distance between the two tapes being at least 4 cm. Between the tapes hair takes a sigmoid form whose number of peaks and number of valleys can be counted. (Figure 2). The higher number is referred to as w (number of waves).
Number of Twists (t). When curly or frizzy hair is fully extended, thicker and thinner parts or constrictions appear (Barbarat et al. 2005). The number of twists (i) equals the number of natural constrictions along the hair axis (Figure 3).
Measurements of CD, i, t, and w were carried out on each collected piece of hair, and at least three hairs (one from each area of the scalp, i.e., vertex, temples, and nape) were characterized for each subject. The mean value of each parameter was used as a descriptor of the hair of a given subject.
The percentage of subjects correctly classified by the segmentation tree analysis was excellent and varied from 100% for type I to 78% for type VIII. For incorrect classifications by segmentation tree analysis, there was never more than one class difference above or below (e.g., type II instead of type III or type IV instead of type III). More interestingly, Table 3 shows the distribution of these typological groups within the different populations.
"African" hairs collected from South Africa, Ghana, and Chicago were mainly classified as types V to VIII Although types VI to VIII prevailed in samples collected from South Africa and Ghana, type V was most frequent in the samples collected in Chicago and likely reflects a past mixed-origin population.
Hairs collected from China were essentially type I and type III. On the other hand, the amount of type III hairs reached 20% in samples from Japan and Korea; type in hair is still more frequent in samples from Thailand, where it is found in one-third of the samples.
Hairs collected from Brazilian volunteers showed a great diversity because they include types I to VI. This is likely the result of past mixed origins, leading to the well-known multiethnic populations.
In three countries (Korea, South Africa, and Ghana), where the cohorts of men and women were well balanced, no sex differences were found.
Some points have to be emphasized. As mentioned, so-called straight hair, as embodied in types I and III, is clearly not exclusive to Asian hair.
Although straight hair is shared by 93% of Chinese, it accounts for 57%, 68%, and 57% of tested Caucasian samples from Denmark, Poland, and Germany, respectively. Such a weight again justifies the initial choice not to include any hair color parameter in our tier approach, because blond hair is a frequent feature in these three countries.
Table 3 depicts some close similarity between Japan, Korea, and possibly Thailand regarding hair type distribution (types I, II, and III). More important, it provides (some) evidence that Chinese hair is different from other Asian hairs.
The same observation applies to African people, because clear shifts in hair type distribution are seen between hairs from South Africans and Ghanaians. Such a preliminary observation should obviously be confirmed by larger studies on African populations.
A great diversity is also observed in Europeans. It thus emerges from hair type classification that the three conventional human subgroups all appear to be heterogeneous. It vindicates the idea that the earlier ethnic distinction between the three racial subgroups (Asian, African, European) is oversimplified and less and less appropriate, especially as far as hair is concerned.
Increasing mixed-race descent and mixed-origin populations have a clear impact on hair type distribution, as reflected by the results on hairs from Brazil and Chicago, the only locations where six hair types were found. Conversely, the more homogeneous frequencies found in Asian countries, mostly limited to three types, suggest a lower statistical weight of past admixture.
The method is simple to use and only needs the measurement of three easily accessible parameters: curve diameter (CD), curl index (i'), and number of waves (w). Even though the method has some limitations (the required hair length must be more than 6 cm (sex bias) and the handling of single hairs may be tricky in some cases (e.g., wave may be mistakenly counted), this method of assigning hair type has a number of advantages. Applied to worldwide human diversity, our method avoids referring to putative, unclear ethnic origin of subjects while providing reliable and relevant data. Briefly, a straight hair type I is a straight hair type I and whether it originates from a European or an Asian subject is not at issue.
So, basically, some standard classifications that can be assigned to hair, no matter whose head it's growing on. One of the comestic companies was paying for it - I'll have to dig through my notes and see if I can find it. 
I think we should come up w/our own terms that incorporate the descriptions that Nappyworm listed. 
They may have been taught that all black hair is basically the same. We were probably all thrown into one category. 
I kinda wanna examine my hair under a microscope now. 
