The biology of African hair
the origin of a human has always had an influence on the styling of the human hair in the cultural dimension. For example, in the case of the African Himba, the hairstyle shows the social status of a member of the community. But the ethnicity of a person also has important implications, for example, when it comes to the planning and procedure of a hair transplantation. Thus human hair is differentiated into three different types, according to the ethnic origin of a person. Hence, Asian, Caucasian and African hair types can be distinguished.
This distinction is made on the basis of the fact that these three hair types differ from each other in terms of characteristic properties. These properties include, for example, the diameter of the hair, the shape of the hair shaft, mechanical properties such as flexibility or brittleness, the combability, the chemical composition of the hair and the keratin contained therein, or the natural moisture of the hair. Depending on which type of hair a person can be assigned to, the named properties vary more or less, with the smallest differences between the three types being, for example, the chemical composition of the hair.
The focus of this article lies, in particular, on the properties of the African hair type, which are compared with those of the other hair types. As you will see, these characteristics have particularly implications when people with an African hair type wish to undergo a hair transplantion. These will be presented to you in the following, as well as the consequences of certain treatment methods, which at the time have been regarded as trends in the procedure of hair transplantation.
Therefore, enjoy reading!!
Yours, Angela Lehmann
The pecularities of the African hair type
Different ethnic origins are always accompanied by a cultural imprint of how the hair is styled to use it as an mean of expression of oneself. In addition, the ethnicity of a person also has important implications for a possible hair transplantion. For this reason, I would like to inform you with my new article about African hair and its specifics as well as the structure of this hair type, and show what might result from this specifics regarding hair transplantation.
Morphological description of African hair compared with other ethnicities
In principle, each human hair is formed out of a hair follicle, which is located in the upper skin and is not visible from the outside. The visible part of the hair, the hair shaft, consists of three different layers. The outermost layer, the cuticle, is also referred to as a scaly layer. In this layer, individual scales lie as in the case of a pine cone. The position of the individual scales relative to one another is important for the natural shining of the hair since it determines the extent of the light reflection. The second layer, the cortex, accounts for up to 80 percent of the hair volume and consists of a high number of individual keratin fibers. This layer is determining the mechanical properties of the hair, such as, the elasticity of the hair. The innermost layer of the hair, the marrow, is also characterized by the presence of keratin fibers; but these are not as strictly ordered as in the cortex. For the following consideration, it must be pointed out again that the hair itself is not transplanted during a hair transplantation, but rather the hair follicle is transplanted from one point of the scalp (donor site) into another (acceptor site) (see also our article The biology of human hair).
The ethnic origin of a person has no influence on the possible length of the hair. On the other hand, the maximum hair length is determined by the age of the person and the type of hair. Thus, in the prenatal or immediately postnatal age, so-called lanugo hairs can be found which have a maximum length of 15 cm and a radius of maximum 20 μm. However, this kind of hair is already replaced immediately after birth by the so-called terminal hair, which can reach a length of up to 60 cm and a radius of up to 60 μm. This type of hair can be found until beginning of puberty (about 12 years). Although terminal hair is also found beyond puberty, it has a different size due to hormonal changes. The terminal hair of an adult can reach a maximum radius of 100 μm up to 1 m (with some exceptions). In addition to the differences between these types of hair, the hair length in the adult age is influenced exclusively by the hair style.
As already mentioned, the diameter varies depending on the type of hair. The smallest and largest measured diameter play an important role as a physical parameter. The African hair type has the largest hair diameter with a range of 55 to 98 μm, for the Asian hair type the values range between 70 and 86 μm and for the Caucasian hair type between 60 and 80 μm. On the other hand, when the hair sections are examined, there are greater differences between the three ethnic hair types. For example, the average sectional area for African hair is about 4,270 μm², for Asian hair it is about 4,800 μm² and for Caucasian hair 3,850 μm², but it must be mentioned that there are also greater variations even within on ethnic hair type (African hair type: 2,200 to 6,500 μm², Asian hair type: 3,000 to 8,000 μm², Caucasian hair type: 1,400 to 6,300 μm²).
Another important property which also varies depending on the type of hair is the hair density on the scalp. It is expressed as the number of hair-forming follicles per square-centimeter scalp. Thus, people with an African hair type show the lowest average value with 161 (± 50) follicles per square centimeter (men: 160 ± 50; women: 163 ± 51). For Asian hair the average value is 175 (± 54) follicles per square centimeter (male: 173 ± 50; female: 178 ± 57); and Caucasian hair type gives an average follicle number of 233 (± 46) follicles per square centimeter of the scalp 211 ± 65, women: 242 ± 77). However, the cited numbers must be seen with a certain caution since, depending on the reference cited these calculations may vary considerably. Thus, for example, the given hair density for men with a Caucasian hair type is source-dependent varying between 192 and 340 follicles per square centimeter of the scalp. More or less large variations in the determination of the hair density also occur when specific areas on the scalp are investigated (vertex, temporal and occipital head). The density of the hair follicles is of great importance, since the density of the existing follicles in the scalp is crucial for which recipient area can later be covered with hair transplants. We shall to return to this point later.
Another important parameter associated with the hair diameter describes the ellipticity of the hair follicle and, consequently, also the property of the curliness of the hair. The ratio of ellipticity to curliness is illustrated in the following scheme.
The ellipticity is calculated source-dependent as the quotient of the largest and the smallest hair diameter. The greater the value of the ellipticity, the more elliptical the hair follicle is shaped and the curlier the hair growing from it is. The highest value of ellipticity is given in the literature as 1.68 for African hair; for Chinese, 1.23 is given. In the middle range are people of Indian origin with 1.40 and Western Europeans with 1.44. It follows that people with African hair have both the most elliptically shaped hair follicles and the most naturally curly hair. These facts must be considered for a hair transplantation, as will be discussed below.
The following figure shows a small tuft of African hair to make the high degree of curliness clear.
As will be described below, the particularly high degree of curliness of African hair is particularly important when volume effects should be achieved with the transplanted natural hair graft.
What do these differences imply for the treating therapist?
The characteristics of the different types of hair described above have some implications for the treatment of people with African hair who want to undergo a hair transplantation. These are discussed in the following.
To begin with – and this applies to all the hair types mentioned – the values with regard to the hair density represent a possible limitation for a hair transplantation. Thus the indicated values are usually slightly rounded off in order to take into account only healthy hair follicles. It follows that with a scalp surface of 600 cm² a person with Caucasian hair has about 120,000 hair follicles (statistically), people with Asian hair have 90,000 follicles and, in the case of African hair, approximately 80,000. From these, however, not all of them are appropriate for a hair transplantation, as this technique has natural limits (see also our article Possibilities and Limitations of Modern Hair Transplantation Techniques).
Regarding the ellipticity of the follicles, the rule of thumb is that the more regular the follicle is shaped, the easier it is for the treating therapist to extract it for transplantation. Accordingly, the extraction of follicles of Asian hair type would be the simplest technically, while the extraction of follicles of African hair type would be significantly more demanding due to the elliptical shape. This is due to the fact that the extraction of the follicles is usually performed with a hollow drill having a circular cross-section. This shape thus corresponds more to that of follicles of Asian hair. In this way it is also possible to explain why the elliptical follicles of people with African hair are more difficult to extract because they can be injured easier during extraction. Injured hair follicles must be regarded as a disadvantage of a method, since no new hair will grow from it, which is contrary to the aim of the treatment.
In the case of a hair transplantation, standard grafts are first taken from the donor area, which are subsequently split into micrografts (see our article on Hair Transplantation). The following figure shows such a micrograft, which represents the fine implant that is transplanted into the acceptor site.
In principle, dark hair is suited best for this procedure, since it is best to recognize for the therapist due to its pigments during the process of splitting. However, as can be seen from the following figure, the splitting of African hair is particularly challenging for the therapist because of the pronounced ellipticity. This makes the follicles difficult to separate from each other without any injury.
Moreover, in the last few years, a trend evolved and some colleagues have moved to extract grafts with special devices which have particularly low drill diameters. Patients with an African hair type should take into account the fact that the ellipticity of the hair follicles makes it very difficult to split them without injury. This is not taken into account, for example, if the extraction is carried out as FUE (follicular unit extraction) with very small drill diameters (for example, 0.7 mm or even smaller). In this case, it must be assumed that in way of extraction particularly many hair follicles are injured.
In principle, however, it can also be said that the number of injured hair follicles can be influenced by the choice of the extraction method. Furthermore, the pronounced ellipticity of the hair follicles is not exclusively disadvantageous for the treatment method. On the contrary, an elliptical hair follicle, as described above, leads to particularly curly hair, which accordingly also produces volume effects even in small amounts, whereby hairless areas on the scalp are covered better. The observation of the pronounced curliness of African hair led to the realization that curly hair basically covers the scalp better than smooth hairs, which resulted in the development of the crosspunch method (see also our article Hair transplantation by using Crosspunch).
Why is the hair transplantation of African hair types a positive challenge?
During my 28 years of experience as a hair transplantation therapist, I have often treated patients with African hair and I know what a great challenge this treatment can be for the therapist. With regard to graft extraction and splitting, special skills are required, which literally can be summarized having a knack for this. If the treating therapist does not have the appropriate skill or experience or uses, for example, FUE with very small drill diameters during his treatment, this can lead to a particularly high number of injured hair follicles, which is in the worst case a failure of the treatment goal. Accordingly, the greatest care is required and patients should be informed about whether a FUE is used for the extraction.
Apart from this, the treatment of patients with African hair type is a great enrichment of my work and I feel this as a special challenge, which I like to meet.
If, after reading this article, you have further questions, for example, if you are personally interested in a hair transplantation, I would recommend you to read the additional articles on my homepage. In addition, I am always at your disposal for a personal discussion in our clinic.
Yours, Angela Lehmann
Franbourg, A., Hallegot, P., Baltenneck, F., Toutaina, C., & Leroy, F. (2003). Current research on ethnic hair. Journal of the American Academy of Dermatology, 48(6), S115-S119.
Loussouarn, G., El Rawadi, C., & Genain, G. (2005). Diversity of hair growth profiles. International journal of dermatology, 44(s1), 6-9.
Sobottka, G. & Weber, A. (2003). Geometrische und physikalische Eigenschaften von Human-Haar. Computer Graphics Technical Reports. [01.10.2017].