Popular as 'natural minoxidil' on the strength of one small trial with no placebo group. Pleasant scent; hair-growth benefit unconfirmed.
Rosemary essential oil is widely promoted for hair growth. The claim traces to a 2015 trial in which 100 people with pattern hair loss used rosemary oil or 2% minoxidil for 6 months: both groups gained some hair, with no difference between them.
That trial had no placebo arm, used low-strength minoxidil, and has not been independently repeated. Rosemary extracts in skin and body products are mostly there as antioxidants that protect the formula.
One small randomised comparison without placebo found similar hair-count changes to 2% minoxidil at 6 months. Without a placebo group it cannot show that either did better than nothing, and it tested a leave-on oil, not a rinse-off shampoo.
100 people with pattern hair loss used rosemary oil or 2% minoxidil for 6 months. Neither changed at 3 months; both had a significant rise in hair count at 6 months with no difference between groups, and scalp itch was more common with minoxidil.