Dandruff: what are the effects of black seed oil?

Key points to remember.

Dandruff results from an imbalance of the scalp, involving both local inflammation and the proliferation of yeasts of the genus Malassezia.
Nigella oil possesses anti-inflammatory properties that are well documented, primarily attributed to the thymoquinone it contains.
Some antifungal effects have also been observed on Malassezia, but only with black cumin oils whose thymoquinone content exceeds that typically found on the cosmetic market.
No clinical study to date has demonstrated an effect of nigella oil on dandruff.
In cases of dandruff, we recommend opting for active ingredients with scientifically proven anti-dandruff efficacy (ciclopirox olamine, piroctone olamine, ketoconazole...).

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Can nigella seed oil exert an effect on dandruff?

The dandruff corresponds to an excessive shedding of the scalp, visible as white or yellowish flakes, sometimes accompanied by itching or discomfort. It results from an accelerated renewal of scalp keratinocytes, often associated with local inflammation and an imbalance of the skin microbiome. Among the microorganisms involved are yeasts of the genus Malassezia, naturally present on the scalp but whose excessive proliferation impairs the skin barrier and accelerates keratinocyte turnover.

The active ingredients used to limit dandruff generally act via two key mechanisms: reducing scalp inflammation and controlling the proliferation of Malassezia.

In this context, the vegetable black seed oil, extracted from Nigella sativa seeds, has attracted interest. Long used in traditional medicine, it is rich in unsaturated fatty acids and bioactive compounds, including thymoquinone. If the black seed oil is primarily recognised for its nourishing benefits, it also exhibits anti-inflammatory and antioxidant properties, which could theoretically help soothe an irritated scalp prone to dandruff.

Mechanistically, the anti-inflammatory effects of the nigella have been extensively studied, particularly when taken orally. A meta-analysis encompassing 20 clinical trials, involving a total of 1,086 participants, shows that supplementation with Nigella sativa allows for the significant reduction of several markers of inflammation and oxidative stress. A marked decrease in C-reactive protein, TNF-α and malondialdehyde, a lipid peroxidation marker, was observed, alongside a significant increase in endogenous antioxidant capacities—such as glutathione peroxidase and superoxide dismutase activities. These data suggest that nigella modulates certain inflammatory pathways, mechanisms that could be relevant in cases of scalp inflammation due to dandruff, although extrapolation to topical use remains open to debate.

However, when considering the effect of nigella oil on Malassezia, the picture is more nuanced. The antifungal properties of nigella are primarily attributed to the thymoquinone it contains. An in vitro study evaluated various Nigella sativa oils with differing thymoquinone and free fatty acid contents in order to assess their antimicrobial activity against several microorganisms, including Malassezia furfur. The results show that the inhibition of Malassezia furfur growth is maximised when the oil contains a high concentration of thymoquinone (around 3%) combined with a low proportion of free fatty acids. Conversely, oils poorer in thymoquinone exhibit markedly reduced antifungal activity. These data confirm that the observed antifungal effect closely depends on the thymoquinone content of the nigella oil.

Zone d'inhibition de Malassezia furfur pour différentes huiles de nigelle contenant différentes concentrations de thymoquinone (TQ) et d'acides gras libres (FFA). Le pyrithione de zinc est ici utilisé comme contrôle positif. — Zone of inhibition of Malassezia furfur for different Nigella oils containing varying concentrations of thymoquinone (TQ) and free fatty acids (FFA). Zinc pyrithione is used here as the positive control.
Source: VON OPPEN-BEZALEL L. & al. Antimicrobial activity by a unique composition of cold pressed Nigella sativa seed (black cumin) oil. Food Science and Nutrition Research (2021).

However, in the nigella seed oils commonly used in cosmetics, thymoquinone is generally present at much lower concentrations, most often below 1%. This low level makes it difficult to extrapolate the results obtained in vitro. In other words, although thymoquinone has demonstrable antifungal activity, it is unclear whether nigella oil, as it is conventionally used, contains enough to exert a significant effect on Malassezia in the context of dandruff.

To date, no clinical trial has assessed the effect of nigella seed oil on dandruff or on scalp flaking associated with the fungus Malassezia.

The available data therefore remain indirect and do not permit a conclusive statement on genuine anti-dandruff efficacy. Moreover, the nigella oil has a relatively viscous and greasy texture, which can render its application impractical on the scalp, particularly in individuals with fine or oily hair. If required, it may be used as a supplementary treatment in very small amounts, for instance a few drops applied locally to the scalp before shampooing, but it cannot replace an anti-dandruff shampoo or treatment containing active ingredients whose efficacy has been demonstrated in various clinical studies.