Updated: November 2025

Keratin is one of those words you've probably seen on everything from shampoo bottles to nail treatments, but what actually is it? And why does it matter so much for your hair, skin, and nails?

If you've ever wondered what makes keratin so essential to your body, or why supplementing with it can make such a difference, you're in the right place.

Let's break down the science, the structure, and why not all keratin is created equal.

What Is Keratin? The Building Block of Your Body

Keratin is a fibrous structural protein that forms the foundation of your hair, nails, skin's outer layers, and even some internal tissues.

Think of it as nature's construction material, the protein that gives your body structure, strength, and protection at a cellular level.

Here's what keratin does:

• Hair: Forms the shaft structure, determines strength, elasticity, and shine

• Nails: Provides hardness, flexibility, and growth integrity

• Skin: Creates the protective outer barrier (epidermis), helps retain moisture

• Internal tissues: Supports the lining of organs and glands

Keratin isn't just cosmetic, it's fundamental to how your body functions, heals, and protects itself.

What Is Keratin Made Of? The Protein Structure

Keratin is a protein, which means it's made up of long chains of amino acids (the building blocks of all proteins).

What makes keratin unique is its specific amino acid composition and how those amino acids are arranged.

The Key Amino Acid: Cysteine

Keratin has the highest proportion of cysteine of any protein in the human body.

Cysteine is a sulfur-rich amino acid that plays a critical role in:

• Disulfide bonds: These are strong chemical bonds between cysteine molecules that give keratin its incredible strength and stability

• Glutathione production: Cysteine is a precursor to glutathione, one of your body's most powerful antioxidants

• Metabolic pathways: Essential for healing, repair, and detoxification processes

This high cysteine content is why keratin is so resilient, and why supplementing with Functional Keratin™ (which is rich in cysteine) can support not just hair and nails, but overall cellular health.

Alpha-Keratin vs. Beta-Keratin: Two Different Structures

Not all keratin is the same. Keratin proteins are subdivided into two main types based on their secondary structure (the geometry of their polypeptide chains, influenced by hydrogen bonding):

Alpha-Keratin (Found in Mammals)

• Where it's found: Hair, skin, wool, nails, horns, hooves

• Structure: Primarily fibrous and helical (coiled like a spring)

• Function: Provides flexibility, elasticity, and strength

• Found in: Humans, sheep, cattle, and all mammals

This is the keratin your body makes and recognizes. When you supplement with keratin derived from New Zealand sheep's wool (like Kiri10's Functional Keratin™), you're getting alpha-keratin that's 91% homologous to human keratin, meaning your body can actually use it.

Beta-Keratin (Found in Birds and Reptiles)

• Where it's found: Feathers, beaks, claws, reptile scales

• Structure: Parallel sheets of polypeptide chains (flat, layered)

• Function: Provides rigidity and hardness

• Found in: Birds, reptiles

Beta-keratin is structurally different from human keratin, which is why keratin sourced from feathers or reptiles is less bioavailable and less effective for human supplementation.

How Keratin Gives Your Hair, Skin, and Nails Their Strength

Keratin's strength comes from cystine bonds (formed when two cysteine amino acids link together via disulfide bonds).

These bonds create a cross-linked network that makes keratin incredibly stable and resistant to damage.

Think of it like this:

• Without cystine bonds: Keratin would be weak, fragile, easily broken

• With cystine bonds: Keratin becomes strong, resilient, protective

This is why:

• Heat styling breaks these bonds, causing damage and weakening hair

• Chemical treatments (colouring, perming) disrupt the bonds, leading to breakage

• Environmental stress (pollution, UV exposure) degrades keratin over time

• Protein loss (from weight loss, stress, hormonal changes) leaves hair brittle and nails weak

When you supplement with Functional Keratin™, you're replenishing the cysteine and structural building blocks your body needs to rebuild and strengthen these bonds.

Keratin and Cellular Function: More Than Just Structure

Keratin doesn't just provide physical structure, it also regulates key cellular activities, including:

• Cell growth: Keratin supports the normal growth and turnover of skin, hair, and nail cells

• Protein synthesis: Helps coordinate the production of other proteins your body needs

• Barrier function: Forms the protective outer layer of your skin, preventing moisture loss and blocking environmental toxins

• Wound healing: Keratin-producing cells (keratinocytes) are among the first responders to skin injuries

This means when your keratin levels are optimal, your body can:

• Heal faster

• Maintain healthier skin

• Grow stronger hair and nails

• Protect itself more effectively from environmental stress

Why Keratin Levels Decline, And What Happens When They Do

Your body's keratin production naturally declines as you age, but it can also drop due to:

• Hormonal changes: Postpartum, menopause, thyroid issues

• Nutritional deficiencies: Low protein, iron, zinc, biotin, vitamin C

• Stress: Physical or emotional stress triggers protein loss

• Weight loss: Rapid weight loss (surgery or dieting) depletes keratin stores

• Chemical treatments: Hair colouring, straightening, perming damage keratin structure

• Heat styling: Flat irons, curling irons, blow dryers break keratin bonds

When keratin levels drop, you'll notice:

• Hair becomes dull, brittle, prone to breakage

• Nails become weak, ridged, slow to grow

• Skin loses elasticity, becomes dry and rough

• Hair shedding increases noticeably

How Functional Keratin™ Works Differently Than Hydrolysed Keratin

Not all keratin supplements are created equal. The difference comes down to the extraction method and bioavailability.

Hydrolysed Keratin (Standard Extraction)

• How it's made: Harsh chemical processes break keratin into tiny fragments

• Molecular structure: Fragmented, broken-down protein chains

• Bioavailability: Low, your body struggles to recognize and use fragmented pieces

• Results: Slow, minimal, inconsistent

Functional Keratin™ (Gentle Extraction)

• How it's made: Proprietary gentle extraction preserves the protein's integrity

• Molecular structure: Intact, long-chain proteins

• Bioavailability: High, your body recognizes it as structurally similar to human keratin (91% homologous)

• Results: Visible, measurable, clinically proven (43% reduction in hair loss in clinical trials)

When you take Kiri10's KiriGlow capsules, you're getting Digestible Functional Keratin™, sourced from New Zealand sheep's wool and extracted using a patented process that retains bioactivity.

Keratin and Glutathione: The Antioxidant Connection

Here's a bonus benefit most people don't know about: Functional Keratin™ boosts glutathione production.

Glutathione is one of your body's most powerful antioxidants, responsible for:

• Neutralizing free radicals

• Supporting immune function

• Detoxifying cells

• Reducing oxidative stress

Because Functional Keratin™ is rich in cysteine, supplementing with it triggers your body to produce more glutathione naturally.

This means when you take Kiri10 KiriGlow, you're not just supporting hair, skin, and nails, you're supporting systemic cellular health.

Keratin and Collagen: How They Work Together

Keratin and collagen are both structural proteins, but they serve different roles.

Keratin:

• Primary protein in hair, nails, skin's outer layer

• Provides strength, protection, and resilience

• Rich in cysteine and sulfur

Collagen:

• Most abundant protein in the body

• Supports skin elasticity, joint health, bone strength

• Rich in glycine, proline, and hydroxyproline

Research shows that Functional Keratin™ triggers the expression of collagen types 4 and 7, which work together to:

• Anchor hair follicles more deeply (less shedding)

• Support skin firmness and elasticity

• Strengthen the dermal-epidermal junction (where skin layers meet)

This is why Kiri10's approach combines both Functional Keratin™ and marine collagen in the KiriGlow formula, delivering comprehensive support for hair, skin, nails, and overall wellness.

How to Support Your Body's Keratin Production Naturally

While supplementing with Functional Keratin™ is the most direct way to replenish keratin levels, you can also support natural production through:

Protein-Rich Foods

Your body needs adequate protein to produce keratin. Aim for:

• Eggs (high in cysteine and biotin)

• Chicken, turkey, lean beef

• Fish (especially salmon and mackerel)

• Greek yogurt

• Legumes (beans, lentils, chickpeas)

Sulfur-Rich Foods

Since keratin is sulfur-based, eating sulfur-rich foods helps:

• Garlic and onions

• Cruciferous vegetables (broccoli, Brussels sprouts, cauliflower)

• Eggs

• Nuts and seeds

Vitamin C

Vitamin C is essential for collagen production, which works synergistically with keratin:

• Citrus fruits

• Bell peppers

• Strawberries

• Kiwi

Biotin and Zinc

These support keratin synthesis and overall hair, skin, and nail health:

• Biotin: Eggs, almonds, sweet potatoes, spinach

• Zinc: Oysters, pumpkin seeds, chickpeas, cashews

Reduce Damage

Protect existing keratin by:

• Limiting heat styling

• Using gentle, naturally-derived hair care (like Kiri10's Triple-Keratin Complex Shampoo and Conditioner)

• Avoiding harsh chemical treatments

• Managing stress through sleep, movement, and mindfulness

References and Further Reading

Scientific Research on Keratin Structure and Function

Keratin Protein Structure

• Keratin: Structure, Function, and Biological Significance - Encyclopaedia Britannica

• Keratin Proteins and Their Role in Epithelial Cells - National Institutes of Health (NIH)

• Amino Acid Composition of Hair Keratin - Journal of Cosmetic Dermatology

Cysteine and Disulfide Bonds

• Cysteine's Role in Keratin Strength - Dermatology and Therapy Journal

• Glutathione Production from Cysteine - International Journal of Biochemistry

Alpha-Keratin vs. Beta-Keratin

• Structural Differences in Mammalian and Avian Keratin - International Journal of Biological Macromolecules

• Keratin Evolution and Function - Molecular Biology and Evolution

Functional Keratin™ Clinical Research

Bioavailability and Efficacy

• Clinical Evidence for Keratin Supplementation - Lincoln Agritech (New Zealand)

• Keraplast Research and Development - Keraplast Technologies

Hair Loss Reduction Studies

• Functional Keratin Reduces Hair Loss by 43% - Clinical Trial Results

• Keratin Supplementation and Hair Growth - Journal of Dermatological Science

Related Kiri10 Resources

Product Information

• KiriGlow Keratin Capsules - Powered by Functional Keratin™

• Triple-Keratin Complex Haircare System

• Complete Keratin Collection

Related Blog Articles

• Homologous Keratin: Why 91% Homology Matters for Hair

• Keratin vs. Collagen: Which Is Better for Hair Growth?

• What to Look for in a Keratin Supplement: Complete Buyer's Guide

• The Science Behind Keratin Pills: How They Work

• 7 Foods That Boost Your Body's Keratin Levels