If hair growth is a top concern for you, then you have probably considered taking either a collagen or a biotin supplement (or both!). These ingredients are everywhere, and it’s nearly impossible to scroll through any social feed without seeing personal anecdotes from people who swear by their supposed hair-growing abilities.

But with so much conflicting information out there, it can be hard to figure out which supplement would actually work best (if at all) for you and your hair needs. So, to settle the debate between collagen and biotin, we turned to the experts. See what they had to say below.

How collagen works for hair growth

Collagen plays a vital role in many parts of the body, including healthy hair growth. As Morgan Rabach, MD, board-certified dermatologist at Rabach Aesthetics, explains it, when our dermal collagen is healthy, hair follicles are better anchored in our scalp to grow. As we get older, our collagen levels decline, and our skin gets thinner. Dr. Rabach says this can then cause circulation to slow down, and hair becomes more prone to breakage and damage.

So, where do collagen supplements come into this? It’s believed they can support hair thickness through the skin-related benefits. New York City–based dermatologist Hadley King, MD, explains that studies show collagen supplements, which are made of collagen peptides that are easier to absorb, and topical products are most proven to improve hydration and strengthen the skin barrier. Because collagen may help support scalp health, it is possible that it might also result in healthy hair growth, but Dr. King says evidence for this is still limited: “The jury is still out.”

Those who have fish, shellfish, egg, or beef allergies should use caution when taking collagen supplements, as they are sometimes made from animal-derived ingredients. She also says that those with kidney disease, conditions that require protein restriction, or who are pregnant or breastfeeding should first consult with their health care provider to be extra safe. Other downsides can include mild bloating, an upset stomach, or an off-putting taste. So, some things to think about before you start integrating collagen supplements into your routine.