What are the active ingredients contained in lemon verbena hydrosol?

Grown in the tropical regions of South America, the lemon verbena is a shrubby plant from the Verbenaceae family. The Gauls regarded it as a sacred herb and used it to "cast spells and predict the future", "break curses and bring joy", according to the texts of Pliny the Elder. Long used solely for culinary purposes, lemon verbena then made its entrance into the therapeutic and cosmetic fields.

Also known as lemon verbena floral water, lemon verbena hydrosol is obtained by steam distillation. It presents itself as a colorless liquid, sometimes slightly opalescent, and has a characteristic fresh and lemony scent. Although the lemon verbena hydrosol is only weakly charged with essential oil, it remains a valuable commodity that can be incorporated into skin or hair care products.

The floral water of lemon verbena contains numerous active ingredients with interesting properties for skin care treatments and haircare.

The floral water of lemon verbena is rich in citral (≈ 50%).

Neral and geranial, the two stereoisomers of citral, make up the majority of the hydrosol of lemon verbena. In addition to having a strong characteristic lemon scent, they possess anti-inflammatory properties. Indeed, a study has shown that geranial inhibits the activity of NLRP3, an inflammasome complex that triggers an inflammatory signaling pathway and the synthesis of pro-inflammatory cytokines (interleukin-1β and interleukin-4).

Another study conducted on mice has highlighted the antioxidant properties of citral. For this, scientists applied a cream containing 1% citral to shaved mice that had previously been exposed to UVB rays for 5 minutes. This experiment was repeated every day for 24 weeks and, in the end, it was observed that the mice on which the cream had been applied had significantly fewer tumors.

From a mechanistic standpoint, citral has activated the transcription factor Nrf2 by dissociating it from its inhibitor KEAP1. This has allowed for an increase in the production of glutathione, a tripeptide involved in the conversion of the oxidized form of ascorbic acid into vitamin C. Glutathione is also capable of neutralizing free radicals through an electron donation, which prevents them from damaging the tissues and cells of the body.

The lemon verbena hydrosol contains nerol and geraniol (≈ 20%).

These two compounds are isomers with anti-inflammatory properties that allow the lemon verbena hydrosol to reduce redness and soothe the skin. It has also been shown that nerol and geraniol possess antimicrobial activity against certain bacteria, such as Escherichia coli or Salmonella enterica. Thus, lemon verbena floral water can be used as an antiseptic. Finally, the geraniol it contains has antioxidant properties and prevents the peroxidation of lipids in the stratum corneum, compounds that contribute to the maintenance of the skin's protective barrier and hydration.

The floral water of lemon verbena contains eucalyptol and alpha-terpineol (≈ 10%).

Eucalyptol, found in various plants, is generally appreciated for its refreshing and spicy scent, similar to camphor. It also has the ability to act synergistically with α-terpineol and to exhibit anti-inflammatory activity. From a biological perspective, these two compounds inhibit the transcription factor NF-κB, which regulates the expression of most of the body's pro-inflammatory proteins.

The lemon verbena hydrosol contains linalool (≈ 1%).

One of the other ingredients found in lemon verbena floral water is linalool, which belongs to the family of monoterpenic alcohols. This compound notably promotes the synthesis of HSP70 proteins (Heat Shock Protein). These proteins ensure the correct conformation of proteins found in the body's cells and help them protect against external stressors (heat, heavy metals, etc.), which could potentially cause inflammatory responses.

By contributing to the inhibition of these reactions, linalool thus has a anti-inflammatory action. Furthermore, this active ingredient is capable of limiting the proliferation of parasites, such as Leishmania amazonensis, responsible for leishmaniasis, and bacteria, like Cutibacterium acnes, involved in the mechanism of acne. The antibacterial properties of lemon verbena hydrosol thus help to prevent and soothe skin eruptions.