What Are Amino Acids? Their Role in Hair, Skin and Nails

Amino acids are best known as the building blocks of protein. But their role goes beyond muscle development. They also form part of the proteins that give hair its structure, help maintain the skin's connective tissue and make up the hard surface of our nails.

Two proteins are particularly relevant: keratin, found in hair and nails, and collagen, an important component of the skin's supporting framework.

Understanding how amino acids contribute to these proteins helps explain why adequate protein intake matters for everyday hair, skin and nail health.

This guide looks at what amino acids do, how they relate to collagen and keratin, and the specific roles of L-cysteine, glycine, L-lysine and L-arginine.

What Are Amino Acids?

Amino acids are small organic molecules that join together to form proteins. The human body uses 20 standard amino acids to make proteins, with each protein's structure and function determined by the sequence in which its amino acids are arranged.

These proteins have many different jobs, from forming tissues to acting as enzymes involved in everyday biological processes. [1,2]

All amino acids share a basic chemical structure containing an amino group, a carboxyl group and a side chain. Differences in their side chains give individual amino acids their distinct properties.

The body obtains amino acids by digesting dietary proteins and can also produce certain amino acids itself.

Amino acids are commonly classified into three groups:

• Essential amino acids: Nine amino acids that the body cannot make in sufficient amounts and must obtain through food. Lysine is one example.
• Non-essential amino acids: Amino acids that the body can normally produce, including glycine.
• Conditionally essential amino acids: Amino acids that may need to be supplied in greater amounts during particular physiological circumstances, such as illness or significant stress. Arginine and cysteine can fall into this category. [1]

This distinction matters because the body depends on an adequate supply of amino acids to produce and maintain its proteins, regardless of whether they come directly from food or are made internally.

What Do Amino Acids Do in the Body?

The main function of amino acids is to provide the materials needed for protein synthesis.

When we eat protein-containing foods, digestion breaks those proteins down into amino acids and smaller peptides. The body then uses the absorbed amino acids to produce the proteins it needs. [1,2]

These proteins contribute to:

• Tissue structure: Forming proteins such as collagen, keratin and elastin.
• Tissue maintenance: Providing materials for the normal renewal and repair of body tissues.
• Enzyme production: Creating proteins that help carry out chemical reactions.
• Cellular communication: Contributing to molecules involved in signalling and other physiological processes.

Some amino acids also have functions beyond protein production. Arginine, for example, is involved in the body's production of nitric oxide, a signalling molecule that helps regulate blood vessel function. [3]

For hair, skin and nails, amino acids are especially relevant because these tissues depend on structural proteins.

How Do Amino Acids Support Hair, Skin and Nails?

Hair, skin and nails have different structures, but they share a reliance on proteins. Two of the most important are keratin and collagen.

Amino Acids and Hair Structure

Hair is made predominantly of keratin, a fibrous protein produced by specialised cells within hair follicles.

Keratin contains different amino acids, including cysteine, which contributes to the chemical bonds that help maintain the hair fibre's structure.

Cysteine is particularly interesting because it contains sulphur. Two cysteine residues can form a disulphide bond, creating a connection between parts of the keratin structure.

These bonds contribute to the mechanical properties of hair, alongside hydrogen bonds, ionic interactions and other molecular forces. [4]

This explains why amino acid composition matters to the structure of hair. However, the presence of an amino acid in keratin does not automatically mean taking more of that amino acid will make hair grow faster or prevent breakage.

Amino Acids and Skin Structure

Skin contains several types of protein, including collagen and elastin.

Collagen is especially important in the dermis, the layer beneath the skin's surface. It forms part of the extracellular matrix, a network that provides structural support to surrounding cells.

One of collagen's defining features is its amino acid arrangement. Glycine occupies every third position along the characteristic collagen protein sequence, allowing its three protein chains to pack closely together. [5]

Lysine and its modified forms also contribute to collagen structure and the formation of connections between collagen molecules.

The body's ability to form and maintain normal collagen depends on several factors, including amino acid availability and sufficient vitamin C.

Amino acids therefore form part of the biological foundation of skin structure, although that does not establish that additional amino acid supplementation will improve skin firmness or reduce wrinkles.

Amino Acids and Nail Structure

The visible nail plate is composed largely of hard keratin.

Like hair keratin, nail keratin contains amino acids that help determine its physical properties. Sulphur-containing amino acids, particularly cysteine, contribute to the disulphide bonds associated with keratin structure.

Nails are produced by cells in the nail matrix, located beneath the skin near the base of each nail.

Normal nail formation requires protein synthesis and adequate nutrition. Amino acids provide the building blocks for this process, while other nutrients have their own functions in maintaining normal tissues.

The relationship is primarily structural: amino acids are constituents of nail proteins, rather than a guarantee that an amino acid supplement will make nails harder or less brittle.

Four Amino Acids and Their Roles in Hair, Skin and Nails

Different amino acids contribute to different biological processes. Four worth understanding in the context of hair, skin and nail nutrition are L-cysteine, glycine, L-lysine and L-arginine.

L-Cysteine: Supporting Keratin Structure

L-cysteine is a sulphur-containing amino acid found in many proteins, including keratin.

Its distinctive feature is its ability to form disulphide bonds. These connections help stabilise keratin structures and contribute to the physical properties of hair fibres. [4]

Cysteine is also present in the keratinised tissues that form the nail plate and outer layers of the skin.

The body can normally synthesise cysteine, although its availability depends partly on other nutrients, including the essential amino acid methionine.

Why it matters: Cysteine contributes to the molecular structure of keratin. This makes it relevant to understanding how hair and nail proteins are formed.

Glycine: A Building Block of Collagen

Glycine is the smallest amino acid and one of the most abundant components of collagen.

Approximately one-third of the amino acid positions in collagen's characteristic triple-helical region are occupied by glycine.

Its small size allows the three collagen chains to fit closely together, contributing to the formation of collagen's distinctive structure. [5]

Collagen is present throughout the body, including in the skin's connective tissue and in structures surrounding hair follicles.

The body can produce glycine, and it is also obtained through dietary protein.

Why it matters: Glycine is a fundamental part of collagen's molecular structure, helping explain its relevance to skin and connective tissue biology.

L-Lysine: Supporting Collagen Structure

L-lysine is an essential amino acid, meaning it must be supplied through the diet.

The body uses lysine to produce proteins, including collagen.

Within collagen, certain lysine residues undergo chemical modifications that are involved in collagen maturation and the formation of cross-links between collagen molecules.

These processes contribute to the organisation and stability of collagen-rich connective tissues. [5,6]

Lysine therefore has a structural role in tissues where collagen is important, including the dermis.

Why it matters: Lysine contributes to normal protein formation and is involved in the molecular processes that help establish collagen structure.

L-Arginine: Its Role in Nutrient Delivery

L-arginine is involved in protein synthesis and several other metabolic processes.

One of its best-studied functions is its role as a precursor to nitric oxide, a molecule produced by enzymes known as nitric oxide synthases.

Nitric oxide is involved in cellular signalling and the regulation of blood vessel relaxation. Through these functions, it contributes to the body's normal regulation of blood flow. [3]

Blood circulation is relevant to living tissues throughout the body, including the skin and hair follicles, because it delivers oxygen and nutrients.

However, this biological pathway should not be confused with evidence that taking an arginine supplement increases blood flow to hair follicles or improves hair growth.

Why it matters: Arginine participates in protein synthesis and nitric oxide metabolism, both established aspects of normal human physiology.

How Do Amino Acids Work with Vitamins and Minerals?

Amino acids provide components for making proteins, but protein production and tissue maintenance also depend on other nutrients.

The relationship is easiest to understand by looking at the different roles nutrients perform, rather than assuming that combining them necessarily produces a greater effect.

Amino Acids and Vitamin C: Collagen Formation

Collagen production requires both amino acids and specific biochemical processes.

Glycine and lysine contribute to collagen's amino acid structure, while vitamin C acts as a cofactor for enzymes involved in collagen formation.

These enzymes help modify certain amino acid residues, including proline and lysine, during collagen synthesis. Such modifications are important for normal collagen maturation and stability. [6]

Vitamin C has an authorised UK health claim:

Vitamin C contributes to normal collagen formation for the normal function of skin. [7]

This describes a recognised nutritional function of vitamin C. It does not mean that consuming additional amino acids will necessarily lead to increased collagen production or visible changes in skin appearance.

Amino Acids, Biotin and Zinc: Keratin and Protein Structure

Cysteine is part of keratin's structure, but the body's ability to produce proteins involves many other nutrients and cellular processes.

Zinc contributes to normal protein synthesis and the maintenance of normal hair, skin and nails.

Biotin, also known as vitamin B7, contributes to normal macronutrient metabolism and the maintenance of normal hair and skin. [7]

These functions are related to nutrition and tissue maintenance, although they do not establish that biotin directly increases keratin production or that combining these nutrients produces a guaranteed cosmetic result.

Related reading: What Is Biotin (Vitamin B7) and What Does It Do for Hair and Skin?

Amino Acids, Copper and Silica: Connective Tissue Structure

Collagen formation also involves processes that take place after the initial protein chains have been produced.

Copper is required for the activity of certain enzymes, including lysyl oxidase, which participates in the formation of cross-links in collagen and elastin.

Copper contributes to the maintenance of normal connective tissues, an authorised health claim in the UK. [7]

Silica, a form of silicon dioxide found in materials including bamboo extract, is also discussed in relation to connective tissue biology.

However, evidence about silicon's nutritional role and the effects of oral silica supplementation is less established than the authorised functions of nutrients such as vitamin C and copper.

It is therefore more accurate to describe silica as an ingredient being investigated for its relationship with connective tissue, rather than claim that it has been proven to strengthen collagen, hair or nails.

These distinctions help clarify how different ingredients relate to tissue structure without overstating what supplementation can achieve.

Amino Acids in Supplements: What Does Zhinava Vitalyne Contain?

Amino acids occur naturally in protein-containing foods, and a varied, balanced diet is the primary way to obtain the nutrients required for normal protein production.

They can also be included in food supplements alongside vitamins and minerals.

Zhinava Vitalyne contains four amino acids selected for their established roles in normal human biology:

These four amino acids are included in a broader formulation of 25 nutrients and other ingredients, including biotin, zinc, selenium, vitamin C, copper, hyaluronic acid and botanical extracts.

Within this formulation, several vitamins and minerals have established nutritional functions. For example, biotin and zinc contribute to the maintenance of normal hair and skin, zinc and selenium contribute to the maintenance of normal nails, and vitamin C contributes to normal collagen formation for the normal function of skin. [7]

Vitalyne provides 10 mg of each of the four amino acids per daily tablet, a total of 40 mg. These amounts are supplementary to the amino acids obtained from everyday food. They should not be interpreted as clinically established doses for improving hair strength, skin appearance or nail hardness.

Vitalyne is designed as a once-daily food supplement, with 60 tablets providing a two-month supply.

As with any food supplement, it should be used according to the product label and should not replace a varied, balanced diet and healthy lifestyle.

Final Thoughts: Why Amino Acids Matter for Hair, Skin and Nails

Amino acids are essential to the way the body builds proteins.

Cysteine helps explain the chemical structure of keratin, while glycine and lysine are important components of collagen. Arginine has additional functions in protein synthesis and nitric oxide metabolism.

Together, these examples show why amino acids matter to the biology of hair, skin and nails.

Getting enough protein from a balanced diet remains the foundation of amino acid nutrition. Vitamins and minerals also contribute to normal physiological functions, including collagen formation and the maintenance of normal hair, skin and nails.

Understanding these roles makes it easier to assess beauty nutrition products on the basis of what their ingredients do biologically, while keeping expectations about supplementation realistic.

Frequently Asked Questions

1. What are amino acids?

Amino acids are organic molecules that combine to form proteins. The body uses them to make structural proteins, enzymes and other molecules needed for normal physiological functions.

2. What do amino acids do for hair, skin and nails?

Amino acids form part of proteins such as keratin and collagen. Keratin is a major component of hair and nails, while collagen contributes to the skin's connective tissue structure. Adequate amino acid availability is necessary for normal protein production.

3. What is the difference between essential and non-essential amino acids?

Essential amino acids must come from food because the body cannot produce enough of them. Non-essential amino acids can normally be made by the body. Some amino acids become conditionally essential under particular circumstances.

4. Which amino acids are found in collagen?

Collagen contains high proportions of glycine, proline and hydroxyproline, along with other amino acids, including lysine. Glycine occupies every third position in collagen's characteristic triple-helical structure.

5. What is the role of cysteine in hair and nails?

Cysteine is a sulphur-containing amino acid found in keratin. It can form disulphide bonds that contribute to the structural properties of keratin fibres in hair and nails.

6. Can amino acid supplements improve hair growth or skin firmness?

Amino acids are necessary for protein production, but that does not mean taking extra amino acids will necessarily improve hair growth or skin firmness. Evidence for a biological role is different from clinical evidence that a particular supplement produces a measurable cosmetic benefit.

7. Which amino acids are included in Zhinava Vitalyne?

Zhinava Vitalyne contains L-cysteine, glycine, L-lysine and L-arginine, each at 10 mg per daily tablet. They form part of a wider daily beauty nutrition formulation containing vitamins, minerals and other ingredients.

Sources and References

1. MedlinePlus. Amino acids [Internet]. Bethesda (MD): National Library of Medicine; [cited 2026 Oct 16]. Available from: https://medlineplus.gov/ency/article/002222.htm

2. MedlinePlus Genetics. What are proteins and what do they do? [Internet]. Bethesda (MD): National Library of Medicine; [cited 2026 Oct 16]. Available from: https://medlineplus.gov/genetics/understanding/howgeneswork/protein/

3. Luiking YC, Ten Have GAM, Wolfe RR, Deutz NEP. Arginine de novo and nitric oxide production in disease states. Am J Physiol Endocrinol Metab. 2012;303(10):E1177-E1189. doi: 10.1152/ajpendo.00284.2012.

4. Breakspear S, Nöcker B, Popescu C. Chemical bonds and hair behaviour—a review. Int J Cosmet Sci. 2024;46(5):806-814. doi: 10.1111/ics.12967.

5. Shoulders MD, Raines RT. Collagen structure and stability. Annu Rev Biochem. 2009;78:929-958. doi: 10.1146/annurev.biochem.77.032207.120833.

6. Rappu P, Salo AM, Myllyharju J, Heino J. Role of prolyl hydroxylation in the molecular interactions of collagens. Essays Biochem. 2019;63(3):325-335. doi: 10.1042/EBC20180053.

7. Department of Health and Social Care. Nutrition and health claims: guidance to compliance with Regulation (EC) 1924/2006 [Internet]. London: GOV.UK; [cited 2026 Oct 16]. Available from: https://www.gov.uk/government/publications/nutrition-and-health-claims-guidance-to-compliance-with-regulation-ec-1924-2006-on-nutrition-and-health-claims-made-on-foods/nutrition-and-health-claims-guidance-to-compliance-with-regulation-ec-19242006