Current scientific literature, including both preclinical mechanistic studies and randomized controlled trials, supports the conclusion that rosemary oil can promote hair growth.
The claim is specific, empirical, and falsifiable, passing Step 0. Preclinical evidence shows rosemary extract inhibits testosterone 5-alpha-reductase, a mechanism relevant to alopecia treatment [0]. Furthermore, recent randomized controlled clinical trials support the efficacy of rosemary oil formulations in improving human hair growth metrics compared to controls [9]. While some reviews note limitations in broader cosmeceutical literature [11], the specific direct evidence for rosemary oil supports the claim.