Plus, the smaller studies above used a combination of essential oils in their experiments, so it’s hard to know how big of a role rosemary, specifically, played in the results. The research also looked at the effects of these oils when applied directly on the scalp—not when they’re mixed in with OTC shampoos, conditioners, or serums with varying formulations. So, just because a hair product claims to be “volumizing” or “lengthening” because it contains rosemary oil, that doesn’t mean it’ll work (though it might smell nice!).
Another major caveat: While rosemary oil led to the same hair growth as 2% minoxidil in the first 2015 clinical trial noted above, the results weren’t that visibly impressive for either treatment. (We’re talking about a subtly noticeable increase in the number of strands filling in versus a suddenly full head of hair). It’s standard practice for dermatologists to prescribe a higher concentration of Rogaine, Carmen Castilla, MD, a board-certified dermatologist and clinical associate professor at the Icahn School of Medicine at Mount Sinai in New York City, tells SELF: “We usually recommend 5% minoxidil, and when you compare 2% and 5%, the latter is significantly more effective.”
How (and when) rosemary oil could theoretically help support hair growth
Right now, there isn’t enough evidence to suggest that rosemary oil can magically fix sparse patches or stop a receding hairline. Even the experts we spoke with aren’t exactly sure how it could work—but they have a few theories.
Rosemary oil (and specifically, the carnosic acid and carnosol in it) has anti-inflammatory and antioxidant properties, which derms believe might help stimulate blood flow to the hair follicles, Lindsey Zubritsky, MD, a board-certified dermatologist at Premier Dermatology and Skin Cancer Center in Ocean Springs, Mississippi, tells SELF. Simply massaging your scalp (with or without rosemary oil) can also play a role in boosting circulation, research shows. “Increased blood flow equals more nutrients to the scalp, which could help with hair growth, strength, and thickness,” Dr. Zubritksy explains.
Another theory, she says, revolves around rosemary oil’s anti-inflammatory and antimicrobial properties, which could possibly help support a “healthy scalp environment.” (An inflamed scalp can weaken hair follicles and potentially result in shedding.)
Again, there’s no concrete science to back any of this up fully, but even if the routine of applying rosemary oil to your scalp does have these effects, all three experts caution that it won’t help all types of thinning or balding. “There are actually various types of alopecia and hair loss,” Dr. Cameron explains—each with different causes that require tailored treatments.
Research shows that people with androgenetic alopecia, for example, might have better luck with topical solutions like minoxidil compared to folks whose shedding is triggered by an autoimmune disorder or another underlying condition. The latter would call for interventions that address the root of the health issue. (In the case of alopecia areata, steroid injections are a common treatment.)
Are there any risks to be aware of when using rosemary oil on your scalp and hair?
If you still want to give it a try, there aren’t many unpleasant side effects to worry about. However, “I would be careful if you have a history of allergic reactions or scalp sensitivity due to conditions like psoriasis or eczema,” Dr. Zubritsky says, since rosemary oil can sometimes cause contact dermatitis, an unpleasant rash that’s triggered when your skin has direct contact with certain irritants or allergens, like essential oils or added fragrances. (This is why you should always patch test any new hair product on a small area of your skin before using it all over your head.)