Rosemary oil for hair care?

Benefit No. 1: Rosemary essential oil cleanses the scalp.

The rosemary essential oil is rich in bioactive compounds that confer potent antimicrobial activity, relevant for scalp hygiene. These include rosmarinic acid, carnosol, rosmanol, and oxygenated monoterpenes such as camphor and borneol. These molecules act at multiple levels to disrupt metabolism, membrane integrity, and replication capacity of micro-organisms. Studies in vitro have shown that rosemary essential oil inhibits several bacterial strains, including Escherichia coli and Cutibacterium acnes, a bacterium also present on the scalp and sometimes involved in certain forms of dermatitis.

Thus, the rosemary essential oil helps to purify the scalp, reducing bacterial proliferation and impurities. This cleansing effect benefits those with scalps that become greasy. It eases oily dandruff and itching linked to a disrupted scalp microbiome. By limiting bacterial proliferation, rosemary oil helps prevent follicle blockage and supports a healthier environment for hair growth.

Benefit No. 2: Rosemary oil soothes the scalp.

Beyond its purifying properties, rosemary essential oil stands out for its soothing potential for sensitive or discomfort-prone scalps. This anti-inflammatory effect rests on the oil’s richness in aromatic molecules, such as eucalyptol (1,8-cineole) and α-pinene. Eucalyptol has been studied for its ability to modulate the immune response. A rat study showed that this terpene inhibits the production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-4, and IL-5) in lymphocytes, as well as TNF-α, IL-1β, IL-6, and IL-8 in monocytes. Recall that lymphocytes and monocytes are two types of white blood cells. α-Pinene completes the oil’s anti-inflammatory profile and acts by blocking the nuclear translocation of the NF-κB transcription factor, a key pathway in the activation of pro-inflammatory genes.

These effects make rosemary essential oil an interesting natural ingredient for relieving sensations of irritation, itching, or redness associated with scalp imbalance, oxidative stress, or daily aggressors (pollution, UV radiation, limescale, tight hairstyles). This oil is valued by those with a reactive scalp, or prone to flare ups of eczema, as a complement to dermatological treatment.

Benefit No. 3: Does rosemary essential oil support hair growth?

Rosemary essential oil offers several hair benefits. Its ability to stimulate growth and prevent shedding has drawn interest, especially among men. This effect relies on multiple mechanisms: a local action on microcirculation that enhances nutrient and oxygen delivery to hair follicles; an indirect anti-inflammatory effect on follicles; and an inhibitory activity on the androgenic pathway involved in hormone-related hair loss. Androgenetic alopecia results in part from excessive conversion of testosterone to dihydrotestosterone (DHT) by the enzyme 5α-reductase. DHT binds to follicle receptors, alters their growth cycle, and causes progressive hair thinning. To counter this process, we use 5α-reductase inhibitors.

Scientists assessed the effect of a hydroalcoholic rosemary extract on this mechanism. Using a mouse model of testosterone-induced alopecia (C57BL/6 mice), daily application of 2 mg of rosemary extract led to a marked hair regrowth after 16 days of treatment, compared with the control group. In vitro, the extract showed substantial inhibition of the enzyme 5α-reductase and reduced DHT binding to its receptors. An active compound in the extract, 12-methoxy-sarcosalic acid, may partly account for this anti-androgenic activity.

However, results on human volunteers were mixed. In a clinical trial involving 100 men with androgenetic alopecia, 10% rosemary essential oil was compared with 2% minoxidil, a drug that stimulates hair growth. After six months of daily application, no change was observed in either group in terms of hair count. These results are unexpected for minoxidil, whose efficacy has been demonstrated in other studies, and do not support the use of rosemary for hair growth.

Despite its promising potential to stimulate hair growth, rosemary essential oil still requires thorough clinical studies.

Comparaison de l'effet de l'huile essentielle de romarin et du minoxidil sur la pousse des cheveux. — Comparison of the effect of rosemary essential oil and minoxidil on hair growth.
Source: SAHEBKAR A. et al. Rosemary oil versus 2% minoxidil for the treatment of androgenetic alopecia: a randomised comparative trial. Skinmed (2015).

Benefit No. 4: Can rosemary oil prevent grey hair?

The gradual appearance of white hair is a complex biological process that depends on genetic and environmental factors. Among these, the oxidative stress plays an important role by targeting melanocytes, the cells that produce melanin. From around age 35, these cells at the base of hair follicles see their activity decline, a phenomenon accelerated by free radicals. By attacking cellular components, including mitochondrial DNA in melanocytes, free radicals cause mutations that alter mitochondrial activity, which then affects the melanogenesis and accelerates the onset of white hair.

Antioxidants—molecules that neutralise free radicals—play a preventive role in the onset of white hair. Rosemary essential oil fits this rationale. It is rich in antioxidant compounds such as 1.8-cineole, α-pinene and β-pinene. These terpenes have demonstrated their ability to trap free radicals in numerous studies, limiting their harmful impact on pigment cells. By preserving melanocyte and mitochondrial integrity, rosemary essential oil could slow hair greying associated with oxidative stress.

This is only a hypothesis for now. The role of free radicals in hair greying is established, and rosemary oil has antioxidant properties. However, no study has yet shown that this natural ingredient can prevent white hair.