Objective The aim of this study was first to demonstrate that a combination of pyridine‐2, 4‐dicarboxylic acid diethyl ester and resveratrol could synergize in vitro on biological pathways associated with hair growth and then to demonstrate the benefit on hair density in a clinical study. Methods The effects of pyridine‐2, 4‐dicarboxylic acid diethyl ester and resveratrol directly on the hypoxic inducible factor‐1α protein (HIF‐1α) and related genes expression were demonstrated on keratinocytes in culture in vitro using western‐blot analysis and real time quantitative polymerase chain reaction analysis. The effect of resveratrol against oxidative stress induced by hydrogen peroxide treatment was studied in hair follicle and hair matrix cells in vitro using the sensitive probe Dichloro‐dihydro‐fluorescein diacetate (DCFH‐DA). Finally, a randomized clinical study on hair density was conducted on 79 Caucasian female subjects to assess the effect of this combination of actives. Results Pyridine‐2, 4‐dicarboxylic acid diethyl ester and resveratrol stabilized HIF‐1a protein and increased the expression of HIF‐1α target genes. Resveratrol significantly reduced the oxygen peroxide‐induced oxidative stress generated in hair follicle and hair matrix cells. The clinical study showed that a topical treatment with the combination significantly increased the hair density on women from 1.5 months. Conclusion In addition to the antioxidant properties of resveratrol, the association of pyridine‐2, 4‐dicarboxylic acid diethyl ester and resveratrol revealed a synergistic effect on the HIF‐1α pathway. The results of the clinical study confirmed the importance of such a combination to increase the hair density.

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