Genomic Variation in Textured Hair: Implications for Holistic Hair Care

Human hair exhibits remarkable diversity, influenced by both genetic and macromolecular factors. This variation is particularly evident in textured hair, especially Afro-textured hair, which presents unique challenges in hair care due to a lack of comprehensive understanding of its distinct properties.

This article delves into the genomic variations in textured hair, examining their implications for developing effective hair care routines. We explore the structure and growth of hair, the role of genetics, and the specific needs of Afro-textured hair, emphasising the importance of personalised hair care approaches.

Hair Structure and the Hair Growth Cycle

To understand the complexities of hair care, it is essential to first understand the structure and growth cycle of hair.

Hair Structure

Hair is a complex fibre comprised of several structural components. The primary building blocks are keratins, fibrous proteins rich in cysteine. The hair fibre is composed of three main sections, as illustrated in

• Cuticle: The outermost layer, consisting of stacked sub-lamellar layers, primarily cross-linked by cysteines and arranged in a scale-like pattern. It protects the hair and regulates lubrication.  
• Cortex: The main part of the hair fibre, providing mechanical support. It contains macro-fibrils made up of a-keratins.  
• Medulla: The central core of the hair fibre, loosely arranged and not always present, especially in finer hair. It contributes to hair’s volume, strength, elasticity, and texture.  

Hair lipids and protein interactions are crucial in determining the overall structure of hair fibres.  

Chemical Bonds and Hair Structure

The structure and shape of hair fibres are maintained by three types of chemical bonds:

• Disulphide Bonds: These are the strongest bonds, formed between cysteine residues of hair keratins, and are essential for maintaining hair shape and providing mechanical strength.  
• Hydrogen Bonds: Weaker than disulphide bonds, they are vital for stabilising the keratin a-helices and play a role in hair elasticity and moisture properties.  
• Salt Bonds: The weakest bonds, formed between amino acid chains, and contribute to hair’s strength.  

Hair Growth Cycle

The hair growth cycle consists of three phases, as shown in

• Anagen (Growth Phase): This phase is characterised by active hair fibre production, with epithelial cell growth leading to thickening, elongation, and pigmentation of the hair shaft.  
• Catagen (Regression Phase): A brief transitional phase marked by the cessation of cell division and regression of the hair follicle.  
• Telogen (Quiescence Phase): The resting phase, during which the hair follicle is dormant.  

Some authors also identify a fourth phase:

• Exogen (Shedding Phase): This phase involves the shedding of old hair and the replacement with new hair.  

Genetics of Hair

Genetic factors significantly influence hair characteristics, including texture. Genome-wide association studies (GWASs) have identified several genes involved in determining hair fibre shape across different ethnic groups. Key genes include:  

• Trichohyalin (TCHH): Involved in cross-linking keratin filaments for mechanical strength.  
• EGF Receptor Feedback Inhibitor 1 (ERRFI1): Regulates signalling pathways associated with skin morphogenesis and keratinocyte proliferation and differentiation.  
• Peroxisomal Biogenesis Factor 14 (PEX14): Controls hair shape.  
• Peptidyl Arginine Deiminase 3 (PADI3): Modulates the folding and activity of structural proteins in hair follicles.  
• Transforming Growth Factor Alpha (TGFA): Influences epithelial development.  
• Wingless-Type MMTV Integration Site Family, Member 10A (WNT10A): Regulates epithelial proliferation and differentiation in hair follicle cycling and development.  
• Fraser Extracellular Matrix Complex Subunit 1 (FRAS1): Involved in cell adhesion and the integrity of the epidermal basement membrane.  
• GATA Binding Protein 3 (GATA3): Controls hair follicles and interfollicular epidermal keratinocytes.  
• Leucine-Rich Repeat-Containing G Protein-Coupled Receptor 4 (LGR4): Activates the Wnt/β-catenin signalling pathway, influencing hair follicle cycling and growth.  
• Keratin Associated Protein (KRTAP)/Keratin (KRT): Major structural components of hair, crucial for keratinisation.  
• Protein Tyrosine Kinase 6 (PTK6): Involved in signal transduction and responses to ultraviolet radiation and inflammation.  
• Ectodysplasin A Receptor (EDAR): Controls hair shaft diameter and hair follicle patterning.  
• Homeobox C13 (HOXC13): Regulates the formation and cycling of hair follicles.  
• Serine Protease 53 (PRSS53): Co-localises with TCHH and is modulated during hair fibre differentiation.  
• Orofacial Cleft 1 Candidate 1 (OFCC1): Plays a role in hair morphology.  
• Late Cornified Envelope 3E (LCE3E): Affects curly hair shape.  

The functional relationships between these biomarkers are illustrated in

Afro-Textured Hair: Challenges and Care

Afro-textured hair, while sharing similarities with other hair types, has distinct biological and physical properties. These differences lead to specific challenges in hair care.  

Unique Structural Variations

Afro-textured hair is characterised by:

• High Curvature: This increases vulnerability to damage.  
• Elliptical Cross-Section: With varying shapes and diameters.  
• Retro-Curvature at the Hair Bulb: Resulting in an asymmetrical S-shaped hair follicle.  
• Higher Density of Disulphide Bonds: Contributing to its unique structure and texture.  

These structural features make Afro-textured hair less resistant to mechanical extension and more prone to breakage.  

Lipid and Moisture Content

Hair lipids, such as fatty acids, ceramides, glycolipids, and cholesterols, form a protective barrier against external factors. Studies show that Afro-textured hair has the highest overall lipid content but often exhibits dryness. This is attributed to its structure, which creates areas of weakness and contributes to moisture loss.  

Alopecia in the Black Population

Alopecia, or hair loss, is a prevalent issue with varying aetiologies among different groups. In Black women, it is often associated with hair care practices such as:  

• Chemical hair straightening.  
• Hair braiding.  
• Tight hairstyles and hair extensions, which can lead to traction alopecia.  

Other forms of alopecia common in this population include:

• Central Centrifugal Cicatricial Alopecia (CCCA): A primary lymphocytic alopecia.  
• Androgenetic Alopecia (AGA): A hereditary condition.  

The Need for Personalized Hair Care

Personalized hair care is essential for Afro-textured hair due to several factors:

• Societal Beauty Standards: These can influence hair product choices and usage, often promoting ideals that do not align with the natural characteristics of Afro-textured hair.  
• Unique Hair Characteristics: The need for specialised care and products to maintain health and manageability, addressing issues like dryness, breakage, and damage.  
• Potential Health Risks: Concerns about harmful ingredients in hair care products, such as endocrine-disrupting chemicals (EDCs), which have been linked to increased health risks.  

Hair Typing Systems

Hair typing systems, like the Walker Typing system, are used to classify hair based on texture and curl pattern. Afro-textured hair falls under Type 4, which includes, as illustrated in Figure 4:  

• Tight corkscrew curls (4a).  
• Wiry curls with sharp angles (4b).  
• Extremely kinky hair with a zigzag pattern (4c).  

These systems help individuals understand their hair type and select appropriate care products and styling methods.  

Sensitivity to Chemical Relaxers and Hair Dye

Afro-textured hair is often treated with chemical relaxers to improve manageability. However, these can pose health risks, including:  

• Increased risk of uterine leiomyomata.  
• Hair damage and hair loss, including CCCA.  
• Scalp irritation and burns.  

Hair dye products also carry risks due to chemicals like aromatic amines, nitrosamines, phenylenediamines, and heavy metals, which can cause skin irritation, allergies, and toxicity.  

The Future of Afro-Textured Hair Care

The growing demand for personalised cosmetic products, especially for darker skin tones and coily hair types, highlights the need for more research and targeted product development. A deeper understanding of the genetics and molecular interactions of Afro-textured hair is crucial.  

Research should focus on:

• Identifying genetic differences between Afro-textured hair and other hair types.  
• Understanding the structure-function biological interaction networks that control hair follicle cycling and hair shaft characteristics.  
• Analysing how gene polymorphisms affect the growth rate, diameter, and mechanical strength of hair shafts.  

Such research can lead to:

• Improved cosmetic products with more effective active ingredients.  
• Better healthcare practices for preventing complications related to hair styling.  
• New-generation products that offer robust protection against damage and moisture loss.  

Conclusion

Personalized hair care is essential for Afro-textured hair. Addressing the distinct requirements of this hair type will empower individuals to embrace their natural hair, promoting health, beauty, and self-confidence. Future research and development in this area are vital for creating effective and safe hair care solutions.