The 28 Types of Collagen Explained

Collagen Biology

28 types identified

The human body produces 28 distinct collagen types, each with specific structural roles. Type I alone accounts for 90% of all collagen and provides tensile strength to skin, bone, and tendon.

Ricard-Blum, Cold Spring Harbor Perspectives in Biology, 2011

Ricard-Blum, Cold Spring Harbor Perspectives in Biology, 2011

View as image

Collagen is the single most abundant protein in the human body, making up roughly one-third of total protein mass. What most people do not realize is that "collagen" is not one molecule but a family of 28 genetically distinct proteins, each encoded by its own gene and each with a specific structural role. Type I collagen forms the cables that give tendons their strength. Type II builds the springy matrix in cartilage. Type IV creates the basement membranes that separate tissues. Type XVII anchors skin cells to the layers beneath them. The diversity exists because different tissues face different mechanical and biological demands, and evolution solved each one with a specialized collagen variant.^[1] This article maps all 28 types, explains which ones matter most, and clarifies why collagen supplements only contain a few of them. For how your body builds collagen from amino acids, see How Your Body Makes Collagen: The Synthesis Pathway Explained.

What All 28 Types Share: The Triple Helix

Every collagen molecule, regardless of type, contains at least one triple-helix domain: three polypeptide chains (called alpha chains) wound around each other in a rope-like structure. The signature amino acid repeat is glycine-X-Y, where X is often proline and Y is often hydroxyproline. Glycine, the smallest amino acid, must occupy every third position because only it fits in the cramped interior of the triple helix.

Beyond this shared feature, the 28 types diverge dramatically in their overall structure, where they are deposited, and what they do. Some form long fibers. Others form flat sheets. A few are embedded in cell membranes with their triple-helix domains projecting outward. The classification system groups them by structural architecture.^[1]

The Big Five: Types I Through V

Five collagen types account for the vast majority of collagen in the body and are the ones most relevant to health, disease, and supplementation.

Type I: The Structural Backbone

Type I collagen is the workhorse of the connective tissue world. It forms thick, tightly packed fibers that provide tensile strength to skin, bone, tendon, ligament, cornea, and the organic matrix of teeth. Approximately 90% of all collagen in the human body is type I.^[1]

In bone, type I collagen fibers provide the flexible scaffolding that hydroxyapatite crystals adhere to, creating the composite material that makes bone both strong and resilient. Konig et al. (2018) demonstrated that specific collagen peptides (derived from type I) improved bone mineral density by 6.7% at the femoral neck and 3.0% at the lumbar spine in postmenopausal women over 12 months, compared to declines in the placebo group. The T-score at the femoral neck also improved significantly.^[2]

In skin, type I collagen fibers form the dense meshwork that gives skin its mechanical strength. Skin collagen content decreases approximately 1% per year after age 30, contributing to wrinkle formation and loss of skin firmness. Aguirre-Cruz et al. (2020) reviewed the evidence for collagen hydrolysates in skin protection, noting that oral and topical collagen peptides can stimulate fibroblasts to produce new collagen.^[3]

Type II: The Cartilage Collagen

Type II collagen is the primary structural protein in hyaline cartilage, the tissue that cushions joints. It forms thinner, more loosely organized fibers than type I, creating a hydrated gel-like matrix that absorbs compressive forces during movement. Type II also appears in the vitreous humor of the eye and in intervertebral discs.

The distinction between hydrolyzed type II collagen and undenatured type II collagen (UC-II) matters for supplementation. Hydrolyzed collagen peptides are broken down into small fragments that serve as building blocks and stimulate collagen synthesis. UC-II contains intact type II collagen molecules that work through a completely different mechanism: oral tolerance, an immune process where the gut-associated lymphoid tissue "learns" to tolerate cartilage antigens, reducing the autoimmune component of joint inflammation.

Type III: The Soft Tissue Collagen

Type III collagen works alongside type I in soft, distensible tissues: blood vessel walls, intestinal walls, and the uterus. It forms thinner fibers that provide structural support with more elasticity than type I alone. The ratio of type I to type III collagen shifts during wound healing and aging, with type III predominating in early wound repair (producing the softer scar tissue) and type I gradually replacing it during tissue maturation.

Type III collagen is also abundant in the dermis of young skin, contributing to its suppleness. The age-related decline in type III relative to type I is one factor in the loss of skin elasticity over time.

Zdzieblik et al. (2015) studied collagen peptide supplementation (containing types I and III) combined with resistance training in elderly sarcopenic men. The collagen group gained significantly more fat-free mass (4.2 kg vs 2.9 kg) and lost more fat mass (-5.4 kg vs -3.5 kg) than the placebo group over 12 weeks.^[4]

Type IV: The Basement Membrane

Type IV collagen does not form fibers at all. Instead, it assembles into flat, sheet-like networks that form the basement membrane: the thin layer separating epithelial cells from underlying connective tissue. Every blood vessel, kidney tubule, and tissue boundary in the body sits on a type IV collagen scaffold.

Mutations in type IV collagen genes cause Alport syndrome, a genetic kidney disease that leads to progressive hearing loss and kidney failure. This disease illustrates how critical type IV is to filtration barrier function: without properly formed basement membranes, the kidney's filtering system breaks down.

Type V: The Fiber Regulator

Type V collagen appears in small quantities throughout the body, typically alongside type I collagen. Its role is regulatory: it controls the diameter and organization of type I collagen fibers. Without type V, collagen fibers grow too large and become disorganized. It is found in hair, placental tissue, and the surfaces of cells.

Type V collagen is also a component of the cornea, where its fine fibers create the precise spacing needed for optical transparency. Mutations in type V collagen are the most common cause of classical Ehlers-Danlos syndrome, a connective tissue disorder characterized by hyperflexible joints and fragile skin.

The Other 23: Specialized Types

The remaining collagen types serve increasingly specialized functions:

Network-forming collagens (Types VIII, X): Type VIII is found in the endothelium of blood vessels and the Descemet's membrane of the cornea. Type X appears exclusively in hypertrophic cartilage zones during bone development, marking the transition from cartilage to bone.

Anchoring collagens (Types VII, XVII): Type VII forms the anchoring fibrils that attach the epidermis to the dermis. Mutations cause epidermolysis bullosa dystrophica, a severe blistering skin disease. Type XVII (also called BP180) is a transmembrane collagen in skin keratinocytes that acts as the mechanical anchor point for the cell to its basement membrane.

FACIT collagens (Types IX, XII, XIV, XVI, XIX, XX, XXI, XXII): FACIT stands for "fibril-associated collagens with interrupted triple helices." These do not form fibers themselves but decorate the surface of fibrillar collagens, regulating fiber spacing, tissue interactions, and signaling.

Beaded filament collagen (Type VI): Type VI forms distinctive beaded microfilaments that bridge between cells and the surrounding matrix. It is particularly abundant in skeletal muscle, where it connects muscle fibers to their surrounding connective tissue. Mutations cause Bethlem myopathy and Ullrich congenital muscular dystrophy.

Transmembrane collagens (Types XIII, XXIII, XXV): These collagens span the cell membrane with their triple-helix domains projecting into the extracellular space. Type XXV (also called CLAC-P) is expressed in brain neurons, and its cleaved ectodomain co-localizes with amyloid plaques in Alzheimer's disease.

Multiplexins (Types XV, XVIII): These collagens contain multiple triple-helix domains separated by non-collagenous segments. Type XVIII is the source of endostatin, a peptide fragment that inhibits blood vessel growth. Endostatin was once a major focus of cancer research for its anti-angiogenic properties.

Why Supplements Only Contain a Few Types

The supplement industry focuses almost exclusively on types I, II, III, and occasionally V and X. This is not arbitrary: these are the types that can be extracted economically from animal tissues (bovine hides, fish scales, chicken sternum cartilage) and that have clinical evidence supporting oral supplementation.

Liu et al. (2015) reviewed collagen extraction and processing methods, noting that the source material determines which collagen types dominate. Bovine and porcine sources yield primarily types I and III. Fish sources yield predominantly type I. Chicken cartilage yields type II.^[1]

The remaining 23 collagen types are present in quantities too small to extract commercially, are too structurally complex to produce synthetically, or lack clinical evidence for supplementation benefits. Some, like type XVIII (the endostatin source), are biologically interesting but have no role as oral supplements.

An important nuance: once collagen is hydrolyzed into peptides (typically dipeptides and tripeptides like Pro-Hyp and Hyp-Gly), the "type" designation becomes less meaningful. The small peptide fragments serve as building blocks and signaling molecules regardless of which collagen type they originated from. The body uses these peptide signals to stimulate its own collagen production across multiple types. For how collagen degrades with age, see Why Collagen Breaks Down with Age: MMPs and Degradation. For the role of structural modifications, see Collagen Cross-Linking: The Stiffening Process of Aging Tissue.

The Bottom Line

The 28 collagen types represent evolution's solutions to the diverse structural demands of different tissues. Five types (I through V) account for most collagen in the body, with type I alone making up 90%. The remaining 23 types serve specialized roles in anchoring, signaling, and tissue-specific architecture. Collagen supplements contain only a few types because of sourcing practicality and clinical evidence, but hydrolyzed peptides may stimulate production of multiple collagen types regardless of their source.

Frequently Asked Questions

How many types of collagen are there?

There are 28 genetically distinct collagen types in the human body, each encoded by its own gene and serving a specific structural role. All share a triple-helix structure but differ in how they assemble and where they are used. Type I alone accounts for approximately 90% of all collagen. The 28 types were cataloged by Ricard-Blum in a 2011 review in Cold Spring Harbor Perspectives in Biology.

What is the difference between collagen type I and type II?

Type I collagen forms thick, densely packed fibers that provide tensile strength to skin, bone, and tendon. Type II collagen forms thinner, more loosely organized fibers in cartilage, where it creates a hydrated gel that absorbs compressive forces in joints. Type I dominates in rigid, load-bearing structures; type II dominates in flexible, pressure-absorbing cartilage. Most skin and bone supplements use type I; joint supplements may use type II.

Which collagen type is best for skin?

Type I collagen is the dominant collagen in skin (approximately 80% of dermal collagen), with type III making up most of the remainder. Collagen supplements for skin typically contain hydrolyzed types I and III from bovine, porcine, or marine sources. Aguirre-Cruz et al. (2020) reviewed evidence showing that oral collagen hydrolysates stimulate fibroblasts to produce new collagen, improving skin hydration and elasticity.

What is type IV collagen?

Type IV collagen does not form fibers. Instead, it assembles into flat, sheet-like networks called basement membranes that separate tissue layers throughout the body. Every blood vessel, kidney tubule, and organ boundary sits on a type IV collagen scaffold. Mutations in type IV collagen genes cause Alport syndrome, a genetic disease affecting kidneys, hearing, and vision.

Does it matter what type of collagen you take?

The source determines the dominant collagen type: bovine provides types I/III, fish provides type I, and chicken cartilage provides type II. For joints specifically, undenatured type II collagen (UC-II) works through immune modulation rather than providing building blocks. However, once collagen is hydrolyzed into small peptides, the type distinction becomes less meaningful because the peptide fragments stimulate your body's own collagen production across multiple types.

What causes collagen type mutations?

Collagen gene mutations cause a range of genetic diseases depending on which type is affected. Type I mutations cause osteogenesis imperfecta (brittle bone disease). Type IV mutations cause Alport syndrome (kidney disease). Type V mutations cause classical Ehlers-Danlos syndrome (joint hypermobility). Type VII mutations cause epidermolysis bullosa (blistering skin disease). Type VI mutations cause Bethlem myopathy (muscle weakness).