Rosemary and onion extract: What research really shows about hair growth

Hair density changes over time — a fact most people eventually notice. For years, rosemary has been considered one of the most studied plant-based remedies in this regard, and is complemented in Radix by onion extract. What does the research actually say, and what does that mean for its use?

Rosemary oil in direct comparison with minoxidil

The most cited study on rosemary and hair growth comes from Panahi and colleagues, published in 2015 in the journal Skinmed. 100 people with androgenetic alopecia (hereditary hair loss) were randomly divided into two groups: one applied pure rosemary oil to the scalp twice a day for six months, while the other used minoxidil 2%, an established hair loss treatment.

After three months, neither group showed a significant change from the baseline. Only after six months did the hair count increase significantly in both groups — and to a comparable extent. However, a difference was observed in terms of side effects: scalp itching occurred more frequently in the minoxidil group than in those using rosemary oil.

What this means: In this study, rosemary oil was on par with an established active ingredient, while apparently being better tolerated. Important for context: the comparison was made with the lower minoxidil concentration (2%), not the more commonly used 5% variant. And six months is the minimum period the study observed — the authors themselves make no claims about what happens thereafter.

Onion extract: a different starting point

The second frequently cited study on the topic is by Sharquie and Al-Obaidi, published in 2002 in the Journal of Dermatology. This study examined raw onion juice for alopecia areata — an autoimmune condition that is distinctly different from the hereditary form of hair loss that rosemary addressed in the first study.

62 people with this form of hair loss were divided into groups: one group applied onion juice to the affected areas twice daily for two months, while the control group used tap water. The onion juice group showed significantly faster and more frequent hair regrowth than the control group.

What this means — and what it does not: The study is small, limited to a specific autoimmune form of hair loss, and has not been replicated on a larger scale to date. It cannot be applied 1:1 to age-related thinning hair, which affects most people. However, it does show that the sulfur-containing compounds in onion extract seem to have a measurable effect on hair growth — the exact mechanism of action has yet to be fully determined.

Why Radix combines both active ingredients

Rosemary is the best-studied and more broadly applicable of the two ingredients for the type of hair loss that affects most people — which is why it forms the basis of Radix. Onion extract is used as a supplement: as an additional source of active ingredients, not as the primary promise.

Neither rosemary nor onion extract replaces a dermatological examination if hair loss occurs suddenly, severely, or in spurts. Anyone who is unsure should have it clarified by a doctor — Radix is intended as a nourishing, supportive routine, not as a medical treatment.

What is realistic to expect

Both underlying studies observed their effects over weeks to months, not days. Anyone who uses Radix regularly — 2 to 3 times a week over several weeks — is following the same timeframe suggested by the research. Faster promises would not be supported by the available data.

Sources: 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. Sharquie KE, Al-Obaidi HK. Onion juice (Allium cepa L.), a new topical treatment for alopecia areata. J Dermatol. 2002;29(6):343-346.