First things first: Collagen does not make up hair.

Collagen is a protein found in the skin, gut, joints, and throughout the body to provide structure and strength. Hair, on the other hand, is predominantly made up of another protein, keratin. (Keratin is also found in your epidermis and nails.) Keratin is a protective protein that acts as a barrier. All proteins are made up of amino acids, often called “the building blocks” of proteins. 

So why is collagen often marketed toward hair health? Well, supplements like collagen powder aren’t actually the full collagen molecule (which would be too large to digest) but rather broken down and hydrolyzed collagen. In this form, it’s actually absorbable amino acids!   

Essentially: The amino acids in collagen supplements can be used by the body to produce other proteins, such as keratin. 

Certified trichologist and founder of Advanced Trichology William Gaunitz, FWTS, told mbg that the primary amino acid that is most helpful is called proline1. Many collagen supplements are transparent about the amino acid profile within their formula, so you can even find options that contain this amino acid and are likely better suited for hair health. 

But it’s not just about the hair fiber itself, collagen can actually support the hair follicle and surrounding area. Rachel Maiman, M.D., board-certified dermatologist at Marmur Medical, notes that research has shown that collagen levels surrounding the hair follicle and bulb increase during the hair growth phase2 (otherwise called the anagen phase).* Then when they go into the maintenance and shedding phase, the collagen disappears.

So if the body can create more collagen, it may be able to support hair in the growth phase for longer. “As our bodies create more collagen, the layers regenerate. This supports our hair follicles by assisting them in reentering the anagen phase and maintaining the hair growth cycle,” says Maiman.* 

Indeed, we often talk about how you can’t have healthy hair without a healthy scalp. “Collagen supports the scalp’s thickness,”* Maiman says. “A thin scalp with insufficient collagen is less robust and less capable of holding the hair follicle bulbs in place.”