Collagen is a structural protein made naturally in the bodies of humans and animals. It forms the connective tissue that holds together skin, bones, tendons, cartilage, and muscles. When you see collagen sold as a supplement or ingredient, it’s extracted from animal tissues, most commonly the skin, bones, and cartilage of cows, pigs, fish, and chickens. There is no plant that produces collagen, though newer lab-made versions are starting to emerge.
Where Collagen Exists in the Body
Collagen is the most abundant protein in mammals, and its fiber-like structure acts as a scaffold that gives tissues their shape and strength. About 90% of the collagen in your body is Type I, which is densely packed into skin, bones, tendons, and ligaments. Type II collagen is found in elastic cartilage, where it cushions joints and absorbs the impact of movement. Cartilage itself is roughly 60% collagen by weight. Type III collagen shows up in muscles, arteries, and organs.
What makes collagen chemically unusual is its amino acid profile. About 33% of its building blocks are glycine and 24% are proline, a concentration far higher than in most other proteins. A significant portion of those proline and lysine molecules get chemically modified (hydroxylated) after the protein is assembled, which is what gives collagen fibers their rigidity and stability.
Animal Sources Used in Supplements
Collagen is naturally found only in animal flesh, specifically in tissues rich in connective fiber. The commercial supplement industry draws from four main sources, each yielding slightly different types of collagen.
- Bovine (cow): Extracted from cowhide, bones, and tendons. This is the most widely available source and provides primarily Type I and Type III collagen. It’s used in powders, capsules, and food-grade gelatin.
- Porcine (pig): Sourced from pig skin, which has a collagen structure very similar to human collagen. Porcine collagen is common in medical and pharmaceutical applications as well as in gelatin production.
- Marine (fish): Made from fish skin, scales, and bones. Fish skin is particularly rich in Type I collagen and is often used because it would otherwise be discarded as waste. Species like catfish, salmon, and cod are common sources.
- Avian (chicken): The chicken sternum (breastbone cartilage) is a primary source of Type II collagen, the type associated with joint support. Chicken cartilage also contains chondroitin sulfate, another compound linked to joint health.
Gelatin, which shows up in everything from gummy candies to capsule coatings, is simply collagen that has been partially broken down. It’s made by boiling animal bones, cartilage, and skin for several hours, then cooling the liquid until it sets.
How Collagen Gets Processed for Supplements
Raw collagen molecules are far too large for your body to absorb intact. To solve this, manufacturers break collagen down into smaller fragments called peptides or hydrolysates. This process, called hydrolysis, uses enzymes or acids to chop the long protein chains into pieces with much lower molecular weights.
Size matters for absorption. Research comparing different molecular weights found that collagen peptides around 500 Daltons (a unit of molecular mass) were absorbed nearly three times more effectively than peptides at 1,000 Daltons in oral tissue models. This is why most supplement labels specify “hydrolyzed collagen” or “collagen peptides” rather than whole collagen. Intact collagen applied to skin or swallowed whole has poor stability and limited absorption through both the gut lining and the skin barrier.
Marine Collagen vs. Land Animal Collagen
Marine collagen has gained popularity partly because it avoids religious or dietary restrictions around beef and pork, and partly because of sustainability claims. Fish collagen is extracted from parts of the fish that would otherwise be industrial waste: skin, scales, and bones. It yields predominantly Type I collagen, the same type that makes up most of human skin.
One practical difference is molecular weight. Marine collagen peptides tend to be smaller than bovine peptides after processing, which may give them a slight edge in absorption. A placebo-controlled trial using low molecular weight collagen from catfish skin found measurable hydrating and anti-aging effects on participants’ skin. Animal studies with collagen from salmon and fish scales have shown increased antioxidant enzyme activity over extended feeding periods, though translating animal results to humans always comes with caveats.
Bovine collagen, on the other hand, offers a broader mix of Type I and Type III, making it a more versatile choice if you’re not specifically targeting skin. It’s also generally cheaper and more widely available.
What About Vegan Collagen?
No plant produces collagen. Full stop. Products marketed as “plant-based collagen” typically contain vitamins and amino acids thought to support your body’s own collagen production (like vitamin C, zinc, and glycine), but they are not collagen.
True vegan collagen does exist in early commercial form. It’s made through recombinant technology: scientists insert the human gene for collagen into organisms like tobacco plants, yeast, or bacteria, which then produce the protein through fermentation. The challenge is getting the structure right. Most expression systems using yeast or bacteria can’t properly hydroxylate the protein the way human cells do, which affects the collagen’s stability and function. Newer plant-based production systems claim to solve this problem, producing properly structured human-identical collagen without any animal involvement. These products are still niche and considerably more expensive than animal-derived options.
Contaminants Worth Knowing About
Because collagen is extracted from animal tissues, it can accumulate trace heavy metals like lead, cadmium, mercury, and arsenic. This is especially relevant for marine collagen, since fish can bioaccumulate metals from polluted water. Reputable manufacturers test for these contaminants and publish results. Typical safety specifications for collagen supplements set limits at or below 0.50 parts per million for lead, 0.10 ppm for cadmium, 0.02 ppm for mercury, and 0.70 ppm for arsenic. Quality products test well below these thresholds.
Collagen supplements are not regulated the same way as pharmaceuticals, so third-party testing certifications (like NSF or USP verification) offer an extra layer of confidence that what’s on the label matches what’s in the product.
Collagen in Whole Foods
Before supplements existed, people got collagen from food. Bone broth, made by simmering animal bones for hours, is essentially a collagen extraction process done in your kitchen. Skin-on chicken, pork skin, sardines eaten whole, and slow-cooked cuts of meat rich in connective tissue (like oxtail, shanks, and short ribs) all deliver collagen naturally.
Your body also builds its own collagen from scratch, using amino acids from any protein source combined with vitamin C, zinc, and copper. Eating a diet with adequate protein and plenty of vitamin C-rich fruits and vegetables gives your body the raw materials it needs, whether or not you ever take a collagen supplement.