Hair fibres consist of three structural layers: medulla, cortex and cuticle. The cortex contains the highest concentration of keratin, providing tensile strength and elasticity, while the cuticle—formed by overlapping keratinised cells—protects the inner layers. Damage to this protective barrier, whether through chemical exposure or nutritional depletion, leads to porosity and loss of shine.

Hair growth occurs in cycles: anagen (growth), catagen (transition) and telogen (rest). During the anagen phase, keratin synthesis is at its peak. Nutrients such as zinc, iron, sulphur and amino acids like cysteine and methionine are critical to maintaining this process. Even mild deficiencies can reduce the anagen period, resulting in slower hair growth and increased shedding.

Nails are horn-like structures made primarily of hard keratin. The nail plate forms in the matrix beneath the cuticle, where new keratinocytes are continuously generated. As they move outward, these cells flatten and harden into dense, protective layers. Adequate nutrition ensures strong, flexible nails, while insufficient keratin production leads to brittleness and ridging.

Although the nail contains less lipid than the skin, hydration and mineral balance remain essential. Calcium, zinc, iron and silica contribute to firmness and resilience, while amino acids and sulphur support keratin’s structural matrix.

Supporting keratin synthesis requires targeted nutrient choices. Key amino acids like cysteine, methionine, proline and serine can be found in:

• Cruciferous vegetables (broccoli, kale, Brussels sprouts) – rich in sulphur compounds that aid cysteine production
• Spinach and asparagus – sources of proline and glutamine
• Avocado – provides healthy fats plus small amounts of cysteine and glutamine
• Berries – deliver antioxidants that protect keratin-forming cells from oxidative damage
• Seaweed and spirulina – concentrated superfoods offering essential amino acids and trace minerals
• Garlic and onions – potent sulphur donors that enhance keratin cross-linking and synthesis

Keratin reflects the body’s internal health more accurately than any cosmetic indicator. For skincare practitioners, encouraging clients to nourish the hair and nails from within is fundamental. Integrating plant-based superfoods, sulphur-rich vegetables and antioxidants into dietary advice enhances keratin production naturally. This approach creates a complete strategy for resilience, repair and long-term integumentary health.