Scientists have identified 28 types of collagen in the human body, though only a handful play major roles in everyday health. Collagen as a whole makes up 30 to 40 percent of all the protein in your body, making it the single most abundant protein you have. Understanding the key types helps clarify why collagen matters for everything from skin elasticity to joint cushioning, and why different collagen supplements come from different sources.
Type I: The Most Abundant Collagen
Type I collagen accounts for roughly 90 percent of all the collagen in your body. It forms densely packed fibers that provide tensile strength, the kind of structural resistance that keeps tissues from tearing or collapsing under stress. You’ll find it in skin, bones, tendons, ligaments, teeth, and the connective tissue surrounding organs.
Because it dominates skin structure, Type I collagen is the type most directly linked to visible aging. Starting in your mid-twenties, your body’s collagen production drops by about 1 percent per year. By age 35, you may have lost roughly 10 percent of your baseline collagen, which shows up as thinner skin, fine lines, and slower wound healing. When people talk about “losing collagen,” they’re primarily talking about Type I.
Type II: The Cartilage Collagen
Type II collagen is the main structural protein in cartilage, the smooth, rubbery tissue that cushions your joints. Unlike the dense, rope-like fibers of Type I, Type II forms a looser mesh that gives cartilage its ability to absorb shock and allow bones to glide against each other without friction. It’s found in the cartilage of your knees, hips, spine, and rib cage.
Its importance becomes obvious when it breaks down. Animal studies in which Type II collagen is absent show severe disorganization of cartilage, with abnormal cell architecture and a collapsing matrix. In humans, the gradual loss of Type II collagen contributes to osteoarthritis. Research dating back to the 1990s found that patients with severe rheumatoid arthritis experienced less joint swelling and tenderness after taking undenatured Type II collagen from chicken cartilage for three months. Since then, studies using collagen from cattle, sheep, blue sharks, and squid have shown similar improvements in both osteoarthritis and rheumatoid arthritis symptoms.
Type III: The Flexibility Collagen
Type III collagen forms fine, flexible networks called reticular fibers. It works alongside Type I collagen but shows up most prominently in tissues that need to stretch and recoil: blood vessel walls, the lining of the gut, the uterus, and skin. It’s also one of the two main collagens in the heart and cardiovascular system.
Type III plays a particularly important role in wound healing. In the early phases of tissue repair, your body ramps up Type III collagen production to form a temporary scaffold. Over time, as the wound matures, this Type III framework gets gradually replaced by the stronger, more rigid Type I collagen. This transition is part of why fresh scars feel softer and more pliable than older ones. Fetal tissue is also rich in Type III collagen, which contributes to the remarkable healing ability of developing skin.
Type IV: The Basement Membrane Collagen
Type IV collagen doesn’t form fibers at all. Instead, it creates a sheet-like mesh that lines the boundary between tissues, forming what’s known as a basement membrane. These membranes act as molecular filters, controlling which substances pass between compartments in the body. The most critical example is in your kidneys, where Type IV collagen helps filter blood. It also lines blood vessels and sits beneath the outer layer of your skin, anchoring it to the tissue below.
Genetic defects in Type IV collagen cause Alport syndrome, a condition that progressively damages the kidneys, hearing, and eyes, illustrating how essential these filtering membranes are.
Type V: The Regulatory Collagen
Type V collagen is found in small amounts throughout many tissues, including the surface of cells, the placenta, and the cornea of the eye. Rather than forming bulk structural fibers on its own, it helps regulate how thick other collagen fibers grow. Think of it as a control mechanism: it sits within Type I collagen fibers and influences their diameter, which in turn affects tissue properties like transparency. The cornea needs extremely thin, uniform collagen fibers to remain clear, and Type V collagen helps make that possible.
How Collagen Types Are Classified
Beyond numbering them I through XXVIII, scientists group collagens by the structures they form. The three major categories cover most of what matters for health.
- Fibril-forming collagens assemble into long, rope-like fibers with a characteristic banding pattern. Types I, II, III, and V all fall into this group. These are the collagens responsible for tensile strength in skin, bone, cartilage, and tendons.
- Network-forming collagens create interlaced, sheet-like meshes instead of fibers. Type IV is the primary example, forming the filtration networks in basement membranes. Types VIII and X also form networks, appearing in specialized locations like the membrane at the back of the cornea and in growth plate cartilage.
- FACITs (fibril-associated collagens) are short collagen molecules that attach to the surface of existing fibers rather than forming their own. Type IX, for instance, cross-links to Type II collagen in cartilage, helping stabilize the structure from the outside. These are less abundant but play supporting roles throughout the body.
Collagen Sources in Supplements
If you’ve looked at collagen supplements, you’ve likely noticed they come from different animal sources. The source determines which collagen types you’re getting.
Marine collagen, derived from fish skin and scales, is rich in Type I collagen. Because Type I dominates human skin, marine collagen is often marketed for skin health. Bovine collagen, sourced from cows, contains both Type I and Type III collagen, giving it a broader profile that’s often recommended for skin, gut, and cardiovascular support. Chicken collagen, typically extracted from cartilage, is the primary commercial source of Type II collagen and is the form most studied for joint health.
Regardless of source, your body can’t absorb whole collagen molecules. Supplements are broken down into smaller peptides during digestion, and your body then uses those building blocks wherever it needs them. You don’t get to direct Type II collagen to your knees simply by swallowing it.
What Your Body Needs to Make Collagen
Your body synthesizes all types of collagen from amino acids, primarily glycine, proline, and hydroxyproline. But it can’t complete the process without vitamin C. This vitamin serves as a required helper molecule for the enzymes that stabilize collagen’s structure, specifically by modifying proline into hydroxyproline, a step that’s essential for collagen fibers to fold and hold together properly. Vitamin C also directly stimulates collagen gene expression, meaning it tells your cells to produce more collagen in the first place.
Without adequate vitamin C, collagen production stalls. This is exactly what happens in scurvy: the body can’t maintain its connective tissue, leading to bleeding gums, skin breakdown, and poor wound healing. You don’t need megadoses to support collagen synthesis, but consistently eating fruits and vegetables that supply vitamin C keeps the machinery running.