Black seed oil and psoriasis: a solution to combat this skin disease?

The psoriasis is a chronic inflammatory skin disease characterised by the appearance of red and thick plaques that flake. This condition can manifest on different parts of the body, such as the scalp, the soles of the feet, the elbows... It is caused by an excessive renewal of the cells of the epidermis and their accumulation, which leads to a local inflammation. Psoriasis is more common in adults and primarily develops between the ages of 20 and 40.

Psoriasis is primarily caused by genetic factors. Indeed, about 30% of cases are linked to familial forms that involve genetic predispositions. The main gene involved in this condition is the PSORS1 locus. Other minor genes also play a role. The genetic variants associated with psoriasis are found in genes related to the immune system, which leads to an immune dysfunction responsible for chronic skin inflammation and overproduction of keratinocytes.

Other factors external can contribute to the development of psoriasis, such as certain medications, streptococcal infections, stress, as well as lifestyle (alcohol consumption, smoking...). Several studies have also established a link between low antioxidant activity in skin cells and the pathogenesis of psoriasis. Indeed, free radicals can act as messengers and influence certain pro-inflammatory cellular signal transduction pathways, such as the MAPK/ERK pathway. Once the ERK proteins are activated by these reactive species, they trigger a cascade of reactions, some of which contribute to an uncontrolled proliferation of keratinocytes. It has also been shown that the expression of the ERK-1 and 2 genes, coding for the ERK proteins, was higher in lesioned psoriatic skin than in non-lesioned skin.

Note : Psoriasis can also have a significant psychological impact and significantly alter the quality of life of patients. That's why it's crucial to manage it as early as possible.

Theblack seed oil, also known as black cumin oil, is a vegetable oil with multiple benefits. Rich in fatty acids, it is most often obtained by cold pressing from the seeds of the black cumin. From an organoleptic point of view, black seed oil presents itself as an amber liquid releasing a spicy fragrance. Used since antiquity, it accompanies individuals suffering from inflammatory diseases, such as acne, eczema, rosacea or even psoriasis, and can alleviate their symptoms. The anti-inflammatory properties of black seed oil are primarily derived from the thymoquinone it contains.

Thymoquinone has the potential to limit the proliferation of keratinocytes, which is overly active in individuals suffering from psoriasis. This is due to its ability to prevent the synthesis of certain pro-inflammatory cytokines, such as interleukins 2, 6 and 1β (IL-2, IL-6 and IL-1β). In addition to playing a role in the immune response, these cytokines act as a growth factor for keratinocytes. Their inhibition therefore allows for a reduction in keratinisation. Furthermore, thymoquinone inhibits the expression of cyclooxygenase (COX), an enzyme that catalyses the transformation of arachidonic acid into prostaglandin H2. Prostaglandins are inflammatory molecules that increase sensitivity to pain.

Furthermore, this property of inhibiting the proliferation of keratinocytes was demonstrated in a study conducted in vivo on rats. These rats presented lesions similar to those caused by psoriasis. The severity of these lesions was evaluated on a scale of 0 to 12, with 0 corresponding to an absence of lesions and 12 to a significant erythema and a substantial thickening of the skin. For ten days, a cream containing black seed oil, dosed at 5 mg/kg for each rat, was applied to the backs of ten rats, while a cream without black seed oil was applied to the backs of ten other rats. At the end of the experiment, the severity score of the lesions was on average 2 in the rats of the "black seed oil" group and 9 in the rats of the "control" group.

Finally, the thymoquinone found in black seed oil has a proven antioxidant activity and protects skin cells from oxidative stress, which is associated with more severe symptoms of psoriasis. Due to the double bonds present in its chemical structure, thymoquinone can specifically neutralise free radicals by donating an electron, before they attack cellular components. It also increases the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase, which are antioxidant enzymes playing a key role in the elimination of free radicals.

• ROSTAMI-YAZDI M. & al. Oxidative stress in the pathogenesis of psoriasis. Free radical biology and medicine (2009).

• ABDELASIS E. & al. Effect of Topical Application of Black Seed Oil on Imiquimod-Induced Psoriasis-like Lesions in the Thin Skin of Adult Male Albino Rats. Anatomical record (2018).

• KIM B. & al. Black Cumin ( Nigella sativa L.): A Comprehensive Review on Phytochemistry, Health Benefits, Molecular Pharmacology, and Safety. Nutrients (2021).