This is the trial sitting underneath most of what gets said online about rosemary oil. Researchers took 100 men with pattern hair loss and split them at random into two groups for six months. One group applied a rosemary oil lotion twice a day. The other applied 2 percent minoxidil twice a day. Hair counts came from standardized close-up photographs, scored by two dermatologists who did not know which group any man was in.

At three months, neither group had changed in a meaningful way. At six months both groups had gained hair. The rosemary group went from roughly 105 hairs to roughly 154 in the counted area, and the minoxidil group went from roughly 101 to roughly 150, with no meaningful difference between them. Scalp itching went up in both groups over the six months. A few things about how the trial was built are worth holding onto. It enrolled 100 men and no women. There was no placebo group, so it compares the two products against each other rather than against doing nothing at all. The minoxidil used was 2 percent, while 5 percent is the strength most people are handed today. It ran in Skinmed, and the authors closed by calling for more research to work out which components of the oil were doing anything.

Here's the study: Panahi Y, Taghizadeh M, Marzony ET, Sahebkar A. Rosemary oil vs minoxidil 2% for the treatment of androgenetic alopecia: a randomized comparative trial. Skinmed, 2015;13(1):15-21. Read it here

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