Does rosemary oil really work for hair growth?

In one randomised trial involving 100 people with hereditary hair loss, rosemary oil produced the same number of new hairs after six months as minoxidil 2%, the well-known hair-growth lotion. After three months, no difference was visible in either group. That is a striking result, but it comes from a single study, and it sets the bar no higher than minoxidil, a treatment that has been available for decades.

One study is not enough to recommend a treatment. A systematic review of eleven clinical trials concludes that rosemary oil 'may be considered', but explicitly describes the quality of the evidence as limited. A network meta-analysis confirmed that rosemary oil performs less well than established treatments such as dutasteride, finasteride and minoxidil. And a Canadian panel of eleven dermatologists explicitly placed rosemary oil on the list of treatments not recommended for hereditary hair loss, alongside caffeine and other herbal formulations.

The compound in rosemary that is theoretically active, carnosic acid, may inhibit the enzyme that converts testosterone into a substance that suppresses hair growth. It also has antioxidant and anti-inflammatory properties. However, these are findings from laboratory research and mechanistic models, not clinical results in humans. Moreover, carnosic acid dissolves poorly and is unstable, making it difficult to incorporate into a product.

One side effect worth knowing: in the randomised trial, both rosemary and minoxidil users experienced scalp itching more often than before treatment. With minoxidil, that itching was more frequent than with rosemary, but rosemary oil is not entirely without discomfort.

Rosemary oil is popular on social media, but a review of hair-loss advice on such platforms concludes that people typically use these products outside medical supervision and that the scientific basis of such claims should be examined critically.