Curly hair is found in people of all races and ethnicities around the world. However, it is more prevalent in certain populations than others. The structure of curly hair can range from loose waves to very tight coils. Genetics play a major role in determining curl pattern and volume. Environmental factors like humidity can also affect the appearance of curly hair. Examining hair structure, genetic ancestry, and demographic data provides insight into which races and ethnicities are more likely to have curly, coiled, or wavy hair.
Hair Structure and Curl Pattern
Human hair consists of an inner core called the medulla, a middle layer called the cortex, and an outer layer called the cuticle. The cortex contains pigment that gives hair its color. It also contains proteins that determine curl pattern. Curly hair has an oval or elliptical cross-section compared to straight hair which is round. The shape of the follicle where hair grows also impacts curl pattern. Curly follicles are more oval or curved than straight follicles.
The degree of curliness is classified into 4 main types:
Type 1 – Straight Hair
Type 1 hair is straight with no curl or wave pattern. This hair type is the most common worldwide.
Type 2 – Wavy Hair
Type 2 hair is wavy, with a loose “S” pattern. The waves can range from barely there to very prominent.
Type 3 – Curly Hair
Type 3 hair has well-defined springy curls ranging from loose spirals to tight corkscrews.
Type 4 – Coily Hair
Type 4 hair has very tight coils that range from soft waves to tight “Z” patterns. This hair type has the most oval or curved follicle shape.
In general, Types 3 and 4 are considered “curly” while Type 2 is wavy. The curl pattern is strongly linked to racial and ethnic background.
Populations with Predominantly Curly Hair
While curly hair can potentially occur in any population, it is more common in certain racial and ethnic groups.
African Descent
Curly and coily hair is a dominant trait in populations of African descent. Most people native to Africa and the African diaspora (Caribbean, Americas) have very curly to coiled hair. The degree of curliness varies within the population from loose curls to tight coils, corresponding to Types 3 and 4.
Tightly coiled hair is a signature trait of sub-Saharan African ethnic groups. The coiled hair structure may have evolved for protection from the intense heat and sunlight of tropical areas. The curved follicle shape found in Africans is rare in other populations.
European Descent
Curly or wavy hair is also relatively common in European populations but is more variable than among Africans. Many Northern and Eastern Europeans have straight hair while Southern Europeans, Jewish populations, and other ethnic groups have higher incidences of wavy or loosely curly hair corresponding to Type 2 and looser Type 3 patterns.
The European gene pool contains variants for both straight and curly hair. Curly forms likely arose due to admixture with Near Eastern or North African populations over millennia.
West Asia/North Africa
People indigenous to Western Asia and North Africa typically have wavy to curly hair. This region served as a bridge between Europe, Asia, and Africa. Therefore, populations reflect a mixture of hair types ranging from straight to loosely curled.
South Asia
Hair types are diverse in South Asia due to it being the convergence point of several ancestral populations. However, curly hair is common among the indigenous peoples of South Asia. Populations like Dravidians and tribals of Southern India, Sri Lankans, and Bengalis often have wavy to tightly curled hair.
Pacific Islands
Most Pacific Islander groups like Melanesians have naturally curly hair ranging from wavy to coiled. The coiled hair types likely reflect ancient ancestry connections with indigenous Australasians and southeast Asians.
Central/South America
Native American and Mestizo populations of Latin America have high frequencies of curly to coily hair. Their ancestry includes mixes of straight-haired East Asians with very curly-haired Africans and indigenous Americans. Most have wavy to curly hair corresponding to Types 2 to 4.
Others
Curly hair can also occur at lower frequencies in East Asia, Circumpolar regions, Polynesia, and Australia. But straight hair predominates in these areas overall.
Genetic Basis of Curly Hair
Several genes have been identified that determine hair curliness. The main ones are:
EDAR
The EDAR gene contains instructions for making a protein called the ectodysplasin A receptor, which is part of a signaling pathway involved in the development of tissues including hair follicles and sweat glands.
Variants of EDAR are linked to increased curliness in East Asians and Native Americans.
TCHH
TCHH encodes a protein called trichohyalin which is abundant in curly hair but less so in straight hair. It provides structural support in curly follicles.
Mutations in TCHH disrupt the hair structure and cause straight hair.
WNT10A
WNT10A encodes a signaling protein called wnt10a that helps determine the shape of the hair follicle. Certain variants are associated with curly hair.
KRT75
KRT75 provides instructions for making a keratin protein present in curly hair. Keratins give hair structure and durability.
Mutations can lead to looser curl pattern.
PADI6
PADI6 encodes an enzyme that acts on hair proteins to promote curliness. Variants alter hair shape and density.
In general, African populations have a constellation of EDAR, TCHH, WNT10A, and PADI6 genes that promote very tight coils. Europeans have variants associated with looser curl patterns. Several genes likely interact to produce the range of hair types seen worldwide.
Prevalence of Curly Hair by Race/Ethnicity
The following table summarizes the distribution of different hair types among major racial and ethnic groups:
| Race/Ethnicity | Straight | Wavy | Curly | Coiled |
|---|---|---|---|---|
| African | 5% | 15% | 40% | 40% |
| European | 35% | 50% | 15% | 1% |
| South Asian | 20% | 40% | 35% | 5% |
| East Asian | 85% | 10% | 5% | 1% |
| West Asian/North African | 45% | 40% | 15% | 1% |
| Pacific Islander | 10% | 30% | 50% | 10% |
| Latino/Mestizo | 20% | 30% | 40% | 10% |
| Native American | 10% | 30% | 50% | 10% |
This table summarizes the prevalence of different hair curliness types among major racial and ethnic groups worldwide. As shown, indigenous sub-Saharan Africans and their descendants have the highest rates of very tight, coiled hair at around 40%. Their lower percentages of straight and wavy hair reflect the predominance of coils and curls in this population.
Europeans have more variable hair types but wavy forms are most common at 50%. Tightly coiled hair is rare. East Asians have mainly straight hair while other groups like South Asians and Latinos exhibit more diverse mixtures of hair curliness. Genetics clearly plays a role in the racial and ethnic variations in curl pattern around the globe.
Environmental Influences on Curly Hair
Genetics determine the basic curliness and coil patterns based on a person’s ancestry. However, environment can also affect the appearance and texture of curly hair. Key influences include:
Humidity
Curly hair absorbs moisture from the air. High humidity causes the hair cuticle to swell, which makes the curls or coils tighter and more defined. Low humidity has the opposite effect, loosening the curl pattern.
Heat Styling
Frequent use of blow drying, straightening irons, and other heat styling can damage curly hair over time leading to a looser curl pattern. Air drying helps maintain natural curl formation.
Chemical Processing
Chemical relaxers and dyes can break down the hair bonds that form curls. Overprocessing leads to a gradual loosening of the natural curl pattern.
Hair Products
Curly hair has special needs like extra moisture. Products that hydrate and reduce frizz will help preserve the natural coil and curl structure.
While genetics predominantly determines curl pattern, lifestyle and styling habits can alter the appearance and tightness of curls to some degree.
Conclusion
In summary, curly and coily hair is most common in people of Native African descent but can also occur in varying frequencies in all major racial groups. Tight coils arose as an adaptation in ancestral African populations and flow outwards with admixture into surrounding regions over generations. Variants in genes like EDAR, TCHH, and WNT10A underlie the differences in hair curliness globally. Both nature and nurture play roles in determining the appearance of curly hair in populations around the world. Understanding the genetic and environmental influences provides insight into why some races have higher incidences of curled hair textures than others.