Mielle’s rosemary oil is $4.97 an ounce on Amazon today. Two percent minoxidil, the drug it was tested against, is $4.77. The whole aisle leans on one 2015 study of 100 people, so here it is, read out loud, next to what dermatologists say about the hair loss most Black women actually have.

This is a buying guide, not medical advice. The study is real; the question is what it tested and for whom.

THE STUDY (Panahi et al., Skinmed, Jan–Feb 2015): 100 people with androgenetic (pattern) alopecia, randomized: 50 on rosemary oil, 50 on minoxidil 2%, for six months, with standardized microphotographic hair counts at baseline, three and six months. Result: no significant change in either group at three months; a significant increase in both at six; no significant difference between rosemary and minoxidil at either point. Scalp itching rose in both groups and was more frequent on minoxidil. Dry hair, greasy hair and dandruff did not change.