Rosemary Oil for Thinning Hair: What the Famous Trial Tested

Rosemary oil is sold as straight essential oil, as ready-mixed scalp serums, and in shampoos and conditioners with rosemary on the front of the bottle. Most of the hair-growth talk around it traces back to one clinical trial from 2015. Read what that trial tested before you decide what a bottle can do for your part line.

What the 2015 trial did

Researchers assigned 100 people with androgenetic alopecia, the hereditary pattern type of hair loss, to rosemary oil or 2% minoxidil, 50 to each group, for six months. Hair counts didn’t change significantly in either group at three months. Both groups had more hair at six months, and the difference between the two groups wasn’t statistically significant. Scalp itching rose in both groups and was more common with minoxidil.¹

The participants were men with androgenetic alopecia.² Female pattern hair loss can look and behave differently, so the result doesn’t transfer automatically to women.

Where the evidence stops

• One trial, one comparison. A 2025 review of herbal hair-loss remedies leaned on this same trial for rosemary and called for well-designed randomized trials with larger sample sizes.³
• The weaker minoxidil. The comparison was 2% minoxidil. Products with 2% or 5% minoxidil are approved for female pattern hair loss.⁴ The trial didn’t test rosemary against the 5% strength.
• Six months. Neither group showed a significant hair count change at three months.¹ A bottle that hasn’t changed anything in six weeks hasn’t failed a fair test, and one that seems to work in six weeks isn’t matching the trial’s timeline either.
• The product you buy isn’t the study product. A shampoo you rinse off after a minute is not a leave-on oil applied as the trial did. Concentration, carrier oil and how often you apply it all vary from bottle to bottle.

Read the label claim

Under FDA⁵ rules, a product that claims to restore hair growth is a drug, even when it is sold like a cosmetic.⁵ A rosemary product sold as a cosmetic can describe appearance, with wording such as “for fuller-looking hair.” If a cosmetic’s label or ads promise regrowth, treat that promise with caution and ask your pharmacist or dermatologist about it.

“Clinically inspired” or “backed by research” on a label usually points back to the same 2015 trial in men. Ask the seller which study they mean and whether it tested their formula.

Protect your scalp

The FDA⁶ notes that many plant materials can irritate skin or cause allergic reactions when applied to it.⁶ Undiluted essential oil on a scalp you massage twice a day is a lot of exposure.

• Follow the dilution and use directions on the specific product.
• If your scalp itches, burns, flakes or turns red, stop and show a pharmacist or clinician what you used.
• Keep the bottle away from your eyes, and store it out of reach of children and pets.
• If you already use a prescribed or over-the-counter hair-loss treatment, ask before layering an oil on top or switching.

Find out why the hair is thinning

The AAD says effective hair-loss treatment begins with finding the cause, and a dermatologist may order a blood test or a scalp biopsy when a disease, deficiency, hormone change or infection is suspected.⁷ Different types of hair loss are managed differently.

If you choose an approved treatment for pattern hair loss, the AAD says minoxidil takes six to 12 months of continuous use to judge, and the benefit fades if you stop applying it.⁴ Bring your rosemary product to that visit and ask whether it fits alongside the plan.

You can say: “I’ve been using this rosemary product for thinning at my part. Can you tell me what type of hair loss this is, and whether this product makes sense with the treatment you’d recommend?”

Hair, Everywhere includes a monthly Hair Log and visit script. Use the log to record what you apply and how often, and take dated photos of your part in the same light so you and your clinician can compare month to month.