Meta-Analysis on Hair Growth and Structure With a Focus on Black Hair By Briana Lawimore
Title: Meta-Analysis on Hair Growth and Structure With a Focus on Black Hair
Introduction:
Although there is an abundance of different hair patterns and textures, there are very few resources that acknowledge the various characteristics of each unique hair texture and structure among ethnicities. Currently, it is publicized that average human hair grows around ½ inch per month; however, these studies on hair growth rates were not inclusive of all races and ethnicities. Most of the research done regarding hair health has only considered Caucasian subjects. There are very limited studies done using hair samples from other racial groups, particularly Black individuals. The extreme lack of diversity in hair-related studies can lead to misinformation and misdiagnosis for underrepresented communities. This meta-analysis aims to address the average hair growth, density, and breakage rates amongst different ethnicities. Also, the information in this analysis will help determine the best hair care regimens and treatments for Black hair. Comparing hair characteristics among different ethnic groups will help take into account that other factors such as race, environment, and age can contribute to hair growth, density, and breakage. Additionally, this analysis establishes that there is no set standard for what defines healthy hair for all individuals, breaking away from European standards. Ultimately this will help individuals set realistic and healthy expectations for their hair.
Methods
For all of the studies used in this analysis, the eligible participant population consisted of individuals from African, Asian, European, Hispanic/Latino, and Indigenous ethnic groups. When considering the race and ethnicity of the participants in these studies, it is important to note that many Hispanic/Latino individuals can come from different ethnic backgrounds. Hispanic/Latino people can have African, European, and/or Indigenous ancestry. The participants in these studies had to be healthy adults between the ages of 18-59 years old with no systemic or cutaneous diseases. The studies used were conducted within a 17-year time span between 1999-2016. The databases utilized to search for this analysis were NCBI, Pubmed, and Science Direct. Keywords and phrases for searching consist of but are not limited to “Hair Growth Rate”, “Hair Growth in Different Ethnicities”, “Black Hair Growth Rate”, and “Hair Breakage in Different Ethnicities”.
Results
Growth Rates
Two studies were used to analyze hair growth rates among different ethnicities and more specifically with the African diaspora. The first study, “Diversity in Human Hair Growth, Diameter, Colour, and Shape. An in Vivo Study on Young Adults From 24 Different Ethnic Groups Observed in the Five Continents”, examined 2,249 volunteers from 24 different ethnic origins ranging in ages from 18 to 35 years old. The hair growth parameters were carried out on the vertex, occipital and temporal regions of the scalp using a phototrichogram technique that measured the growth of individual hairs in micrometers (μm) per 24 hours. These measurements were later converted to inches per month (month =30 days). The second study, “African Hair Growth Parameters” examined 38 volunteers from West Africa ages 18-59 years old. This study utilized the same hair growth parameters and phototrichogram technique mentioned above. The researchers of this study compared their results with hair growth data from a Caucasian population of 45 subjects ages 19-37 years old.
Based on the results of these two studies, individuals of Asian descent have the highest hair growth rates while individuals of African descent have the lowest hair growth rates. Japanese individuals had the highest rate of hair growth at 0.50433 inches per month while South African individuals had the lowest rate at 0.321261 inches per month. The order of hair growth rates from highest to lowest amongst the ethnicities analyzed in these two studies is as follows: Asian> European> Hispanic/Latino> African. Although the standard for human hair growth has been said to be ½ inch per month, the majority of the ethnicities studied hair growth rates were actually less than this rate. Only Korean and Japanese ethnic groups' hair growth rates were exactly ½ inch per month or higher.
Hair Growth Phases
The hair growth cycle consists of three phases: anagen, catagen, and telogen. Anagen is the growing phase and the longest phase of the hair growth cycle. Catagen is the transition phase of the hair growth cycle in which hair growth begins to slow down and hair follicles shrink. Lastly, telogen is the resting phase of the hair growth cycle and during this phase, hair begins to shed. However, this meta-analysis only focuses on the anagen and telogen phases of the hair growth cycle. The studies utilized to discuss hair growth phases for this analysis are “Diversity in Human Hair Growth, Diameter, Colour, and Shape. An in Vivo Study on Young Adults From 24 Different Ethnic Groups Observed in the Five Continents”, “African Hair Growth Parameters”, and “Hair Density in African Americans”. For “Hair Density in African Americans'', this study collected 4 mm (millimeter) punch biopsy specimens of the scalp of 22 African American and 12 Caucasian patients.
Looking at the telogen phase specifically will help determine the amount of hair that may be shedding within each prospective ethnic group. For “Diversity in Human Hair Growth, Diameter, Colour, and Shape. An in Vivo Study on Young Adults From 24 Different Ethnic Groups Observed in the Five Continents”, Danish, Polish, and Scottish ethnic groups had the lowest percentage of hair at a given time in the telogen phase at 8% while Thai had the highest percentage of hair in the telogen phase at 14%. From the samples of hair collected in the study “Hair Density in African Americans”, African Americans had 5.14% of hair in the telogen phase while Caucasian Americans had 4.23% of hair in the telogen phase. Finally, for “African Hair Growth Parameters”, West Africans had 18% of hair in the telogen phase and Caucasian Americans had 14% of hair in the telogen phase. From the data observed there is no direct correlation between ethnicity and the telogen phase. However, individuals of European descent tend to have less hair in the telogen phase, followed by a mixture of Asian and Latino/Hispanic ethnicities, then African ethnicities.
Studying the anagen phase is useful for determining the amount of hair that is actively growing on our scalp. Unfortunately, only one study (“Hair Density in African Americans” ) used in this meta-analysis discussed the anagen phase. From this study, the average number of hair in the anagen phase per 4 mm punch biopsy for African Americans is 17.3 hairs out of 21.4 hairs in total. This correlates to 80.84% of hairs in the anagen phase. The average number of hair in the anagen phase for Caucasian Americans is 28.8 hairs out of 35.5 hairs in total. This correlates to 81.13% of hairs in the anagen phase. Although, individuals of African descent tend to have lower hair density than other ethnic groups, particularly European ethnicities, the amount of hair in the anagen phase was relatively the same between these two groups.
Volume/Density
Hair density is defined as the number of individual hair strands per square inch on your scalp. Three studies were utilized to analyze the difference in hair density amongst different ethnic groups: “ Diversity in Human Hair Growth, Diameter, Colour, and Shape. An in Vivo Study on Young Adults From 24 Different Ethnic Groups Observed in the Five Continents”, “Hair Density in African Americans”, and “African Hair Growth Parameters”. Among the ethnicities studied in “Diversity in Human Hair Growth, Diameter, Colour, and Shape. An in Vivo Study on Young Adults From 24 Different Ethnic Groups Observed in the Five Continents” Caucasian Australian had the highest density at 225 hairs per centimeter squared (cm2) while South African had the lowest density at 153 hairs per cm2. In “Hair Density in African Americans”, researchers determined hair density from the average number of hair follicles per 4-millimeter punch biopsy. From the samples in this study, the average number of hair follicles for African Americans was 21.4 hairs and for Caucasian Americans 35.5 hairs. Lastly, for the study “African Hair Growth Parameters” the average hair density for West Africans was 190 hairs per cm2 and the average hair density for Caucasian Americans was 227 hairs per cm2. Based on the data of all three studies, individuals of European descent tend to have higher hair density while individuals of Asian and African descent tend to have lower hair densities.
Breakage
Curly and coily hair is known to be more fragile and prone to breakage than straight-texture hair. Therefore, it is important to examine what factors contribute to hair breakage in curly and coily textures to help promote strong and healthy hair. Two studies were used to determine hair breakage rates and factors specifically in Black individuals: “Understanding Breakage in Curly Hair” and “Hair Breakage in Normal and Weathered Hair: Focus on the Black Patient”. In the study “Understanding Breakage in Curly Hair”, researchers collected samples of virgin hair from female African American volunteers and utilized a tensile test to observe how much tension causes breakage in afro-textured hair. This test included a series of controlled mechanical stresses that were applied to 10-millimeter hair sections and consisted of four stages that increased in intensity. The results indicated that cuticle lifting is more prominent closer to the tip of the hair than the root since the root of the hair has less grooming history than the tip. Also, cuticle lifting became permanent after the last and most intense tension application (stage four); however, the cuticle returned to its original form after stages 1-3. This indicates that after a hair strand has experienced intense strain like in stage 4 cracks can form and migrate up the hair strand causing breakage. The article, “Hair Breakage in Normal and Weathered Hair: Focus on the Black Patient” discusses several factors that promote hair breakage, particularly in afro-textured hair. Some of these factors include excessive hair combing and manipulation, heat styling, chemical straightening agents such as relaxers, and twisted hairstyles like locs.
Conclusion
This meta-analysis confirms that there is no set standard that can be applied across all ethnic groups for determining hair health by measuring hair growth, density, and breakage. Rather, there is a wide range of different hair characteristics that is unique to certain ethnicities and hair textures. Based on the data from the articles discussed in this analysis, individuals of African descent tend to have lower hair growth rates, fewer hairs in the anagen phase, and lower hair density in comparison to other ethnic groups. This information can help debunk the stigma that afro-textured hair does not grow or is difficult to manage. Afro-textured hair does grow just at a slower rate than other ethnicities. Therefore, individuals should not compare their hair growth journeys to others because there are several genetic factors that we cannot control that are linked to hair growth rates and density. However, when considering healthy hair growth it is crucial to maintain a good hair regime that will not promote breakage and will help retain length. Especially for individuals with curly, coily, and kinky hair, it is recommended to avoid excessive heat, chemical straighteners, and over-manipulation in order to ensure that your hair strands are healthy and strong.
References:
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