Oh JY, Park MA, Kim YC · Toxicol Res · 2014Animal study (mice)
In shaved mice, 3% peppermint oil applied for 4 weeks produced more hair growth, deeper and more numerous follicles than saline, jojoba oil or 3% minoxidil. No human data.
Mint gives toothpaste its taste and shampoos their tingle via cooling receptors. It freshens; hair-growth claims rest on one mouse study.
Peppermint oil is steam-distilled from the peppermint plant; menthol is its main cooling component. Both trigger the skin's cold receptors (TRPM8), producing the fresh, tingling feeling in toothpaste, mouthwash and 'invigorating' shampoos. The tingle is a sensation, not a sign that anything is being cleaned or stimulated.
At higher strengths menthol is a regulated counter-irritant in pain-relief rubs; in oral and hair care it is used at low levels.
Mint's role in oral care is flavour and a feeling of freshness, which is not the same as reducing bad-breath bacteria. The widely shared claim that peppermint oil grows hair comes from a single 2014 study in mice; there are no controlled human trials.
In shaved mice, 3% peppermint oil applied for 4 weeks produced more hair growth, deeper and more numerous follicles than saline, jojoba oil or 3% minoxidil. No human data.