Proanthocyanidins, particularly those derived from grape seeds (grape seed proanthocyanidin extract, or GSPE), have been investigated for their potential to support hair growth and treat hair loss or thinning. The scientific rationale is primarily based on in vitro and animal studies. For example, a 1999 study published in Phytotherapy Research demonstrated that proanthocyanidins could promote hair follicle cell proliferation and induce the anagen (growth) phase of the hair cycle in mice. The proposed mechanisms include antioxidant effects, modulation of growth factors, and anti-inflammatory properties, which may help improve the microenvironment around hair follicles and support regrowth.

However, robust clinical evidence in humans is limited. A few small-scale or preliminary trials and some topical formulations containing proanthocyanidins have been reported, but large, high-quality randomized controlled trials are lacking. As a result, while there is a scientific basis and some early research supporting the use of proanthocyanidins for hair loss, the overall strength of evidence is low, and it is not yet considered a standard or proven treatment for this condition.