Collagen isn’t one molecule — it’s a family of 28 distinct proteins, each with a different structure and function. If you’re supplementing with collagen, knowing which types you’re taking and why matters more than most labels suggest.
Type I: The Structural Backbone
Type I collagen makes up roughly 90% of the collagen in your body. It’s the primary structural protein in skin, tendons, bones, ligaments, and the organic matrix of teeth. When people talk about collagen for skin elasticity or wound healing, they’re usually talking about Type I.
This is the most abundant form and the most studied. Marine collagen supplements are predominantly Type I, sourced from fish skin and scales. Bovine collagen from hides is also primarily Type I, though it often contains Type III as well.
Type II: Joint Cartilage
Type II collagen is the main structural component of cartilage — the flexible tissue that cushions joints. It’s structured differently from Type I, forming a mesh that gives cartilage its shock-absorbing properties. Supplements targeting joint health typically feature undenatured Type II collagen (UC-II), which works through a different mechanism than hydrolyzed collagen. Rather than providing building blocks, UC-II is thought to modulate the immune response in joints by oral tolerization — small doses teach the immune system not to attack joint cartilage.
The clinical data on UC-II for joint comfort is interesting. A 2016 study published in the International Journal of Medical Sciences found that 40mg of UC-II daily outperformed a combination of glucosamine and chondroitin on multiple joint function measures over 180 days. The mechanism is immunological rather than structural, which is why the effective dose is so much smaller.
Type III: Alongside Type I
Type III collagen is found alongside Type I in skin, blood vessels, and internal organs. It’s particularly important in the early stages of wound healing — your body produces Type III first, then gradually replaces it with Type I as the tissue matures. Bovine collagen supplements from hides typically contain both Types I and III, which is why they’re often marketed for skin health.
Types V and X: The Supporting Cast
Type V collagen helps regulate the diameter of Type I and III fibrils. It’s found in cell surfaces, hair, and the placenta. Type X is associated with the growth and repair of articular cartilage and is involved in endochondral ossification — the process by which cartilage is gradually replaced by bone during development.
These types rarely appear in isolation in supplements. They show up in multi-collagen blends, usually derived from chicken sternum cartilage or eggshell membrane.
Hydrolyzed vs. Undenatured vs. Gelatin
The form matters as much as the type. Hydrolyzed collagen (collagen proteins) has been broken down into smaller chains for absorption through the gut lining. This is the most common form and the one studied for skin, nail, and general connective tissue support. Undenatured collagen retains its triple-helix structure and works immunologically, not as a building block. Gelatin is partially hydrolyzed collagen that gels when cooled — it’s functional in cooking but less bioavailable as a supplement.
What This Means for Your Stack
If you’re supplementing collagen, match the type to the goal. Skin and general connective tissue: hydrolyzed Types I and III. Joint health: undenatured Type II (UC-II), not hydrolyzed. Multi-collagen blends cover more bases but dilute the dose of each type. And regardless of the type, vitamin C is a required cofactor for collagen synthesis — without adequate C, supplemental collagen has less to work with.
Read the label. Know the type. Match it to what you’re actually trying to improve.