Peptides are short chains of amino acids that serve as signaling molecules in the body, and their use in hair loss or thinning treatments is supported by some preliminary scientific evidence, though the data is not robust. Several types of peptides (such as copper peptides and certain biomimetic peptides) have been researched for their ability to stimulate hair follicle growth, improve scalp health, or reduce inflammation.

Copper peptides, for example, are thought to promote angiogenesis (the formation of new blood vessels), increase the size of hair follicles, and prolong the anagen (growth) phase of hair. Some laboratory and animal studies have shown positive effects, and there are small human trials and anecdotal reports suggesting benefit. Other peptides may work by stimulating key growth factors (like VEGF or IGF-1) or by blocking the effects of DHT, a hormone implicated in hair loss.

However, high-quality, large-scale randomized controlled trials in humans are lacking, and most evidence comes from in vitro studies, animal research, or small pilot human studies. Therefore, while there is a scientific rationale and some supporting data, the overall evidence is limited and not conclusive. Peptides are found in a variety of topical hair products, but their efficacy remains an area of ongoing research.