Rosemary essential oil, useful against psoriasis?

The psoriasis is a chronic inflammatory disease that primarily affects the skin and joints. It presents as red, thick plaques that shed. Psoriasis is characterised by an excessive renewal and accumulation of epidermal cells, leading to a local inflammation. Indeed, immune cells (T lymphocytes) are found in the skin and produce inflammatory molecules (cytokines Il-17, Il-22, TNF-α, IL-1β ...) that stimulate the proliferation of keratinocytes. The renewal period of these cells, normally three weeks, is then reduced to three days. This results in an accumulation of immature keratinocytes on the skin surface, increasing the thickness of the outer layer (the cornea). This is referred to as hyperkeratosis.

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. Other factors external can contribute to the development of psoriasis, such as certain medications, streptococcal infections, stress, as well as lifestyle (alcohol consumption, smoking...).

The skin symptoms of psoriasis can affect any area of the body, from the ears to the tongue, including the genital areas which can lead to various clinical forms. However, the scaly plaques are generally located on the scalp, elbows and knees. They are sometimes accompanied by a rheumatism.

Theessential oil of rosemary is extracted from the aromatic plant Rosmarinus officinalis, more commonly known as rosemary. This essential oil is obtained by steam distillation of rosemary leaves. It has been widely used since ancient times for its medicinal and aromatic properties, particularly to relieve rheumatic pains, stimulate blood circulation, and soothe digestive disorders. Today, rosemary essential oil is used in aromatherapy for its numerous skin benefits, such as its anti-inflammatory, antibacterial, and antioxidant properties.

The eucalyptol and borneol found in rosemary essential oil can limit the proliferation of keratinocytes, which is excessive in individuals suffering from psoriasis. This is due to their ability to inhibit the synthesis of certain pro-inflammatory cytokines, such as TNF-α, IL-1β, and IL-6. In addition to their roles in the immune response, these cytokines also act as growth factors for keratinocytes, the cells that make up the outer layer of the skin. By inhibiting these cytokines, the keratinisation process of the skin can be reduced. Furthermore, studies have shown that camphene, present in rosemary essential oil, has anti-inflammatory properties by inhibiting prostaglandin E2, which is linked to the inhibition of cyclooxygenase (COX). Prostaglandins are inflammatory molecules that increase pain sensitivity.

Rosemary essential oil possesses antioxidant properties that may be beneficial for combatting oxidative stress, which is associated with more severe symptoms of psoriasis. Indeed, 1,8-cineole, α-pinene, and β-pinene are three components of this essential oil that have free radical scavenging activity. Their role is to neutralise free radicals, which are unstable molecules with a free electron, by donating a free electron to them.

Thus, the essential oil of rosemary can help to alleviate certain symptoms of psoriasis such as itching or irritation and slow down the keratinisation process. However, it should be noted that no study has proven its beneficial effect on psoriasis.

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