What are the benefits of nettle extract on hair?

The nettle is a plant belonging to the Urticaceae family. Known for its stinging properties, it is also a valuable ingredient in cosmetics. Among the many species of nettle that exist, the dioecious nettle, or Urtica dioica, is the most commonly used in skin and hair care. This plant has been used since antiquity for its hair benefits. Indeed, the Egyptians already used it to promote hair growth and make it shinier. The use of nettle in hair applications continued during the Middle Ages, where this ingredient was included in ointments designed to prevent hair loss.

Nettle continued to be used in hair care during the Renaissance but was somewhat relegated to the background with the advent of the industrial revolution. Indeed, chemical and scientific advancements favored the use of mass-produced shampoos made from newly synthesized molecules. Today, nettle is regaining its prestige due to the growing desire of consumers to turn towards natural products.

Thenettle is often incorporated into shampoos or treatments for oily scalps due to its sebum-regulating properties. This ingredient acts on the sebaceous glands by inhibiting 5-α-reductase, the enzyme that catalyzes the transformation of testosterone into dihydrotestosterone (DHT). The binding of DHT to a cytosolic receptor in the sebaceous glands leads to an intensification of sebum production. By inhibiting this process, nettle thus helps to combat oily hair. Regular use of a hair care product containing nettle can help individuals whose hair quickly becomes greasy to control sebum production at the scalp level and may allow them to space out their shampoos.

Nettles contain polyphenols, compounds with antioxidant properties. These molecules can neutralize free radicals by donating an electron before they weaken the hair bulb and hair fibers, thus promoting the appearance of split ends. Therefore, applying nettle to the hair has a protective effect on the hair and limits the effects of exposure to UV radiation and pollution, elements that generate oxidative stress.

Furthermore, it can be assumed that the antioxidant properties of thenettle allow it to slow down the graying process, or the whitening of hair, which a study has shown to be correlated with the presence of free radicals. Indeed, although the mechanism by which these operate at the level of hair fibers remains poorly understood, it seems that free radicals could trigger a chain reaction leading to the degradation of melanin, the pigment that gives hair its color.

Note : this is based on indirect evidence, as no study has demonstrated that nettle itself prevents the occurrence of split ends and white hair.

Nettle extract acts on scalp inflammations by soothing irritations and reducing itching sensations. Its anti-inflammatory properties operate at various levels within cells. Notably, nettle is capable of inhibiting 5-lipoxygenase, an enzyme that plays a key role in the metabolism of arachidonic acid. This acid, in turn, stimulates the activity of cyclooxygenases COX-1 and COX-2, molecules that catalyze the formation of prostaglandins, which are inflammatory mediators.

It has also been demonstrated that nettle inhibits the NF-κB pathway, which is involved in immune and inflammatory responses. Studies in vitro have also proven that this ingredient downregulates the release of interleukins IL-2 and IL-1β and the tumor necrosis factor TNF-α. These are pro-inflammatory cytokines, which are also involved in irritations and itching.

Affecting one in two people, dandruff is a common hair disorder. Several factors have been identified as contributing to the onset of dandruff, among which is an overgrowth of Malassezia type fungi. By hydrolyzing the triglycerides present in sebum, these pathogens are responsible for the production of pro-inflammatory mediators. In addition to helping fight inflammation, nettle extract has a antifungal activity against these fungi, which is attributed to the polyphenols it contains.

A study has particularly focused on the anti-dandruff effects of nettle. Over a period of five weeks, three times a week, 60 individuals with dandruff applied a shampoo containing piroctone, climbazole, and extracts of nettle, chamomile, rosemary, sage, peppermint, and wheat germ. At the end of the five weeks, the researchers observed that 80% of the participants no longer had dandruff and that 20% had significantly less. Although the shampoo contains several active ingredients, the scientists attribute a large part of its effectiveness to the nettle extract.

Studies have also highlighted that nettle can help reduce hair loss. In one such study, 120 individuals suffering from androgenetic alopecia and telogen effluvium applied a shampoo and serum containing nettle extract for six months. At the end of the six months, researchers noted a 90% decrease in their hair loss, compared to a 40% decrease in participants who received placebo treatments.

This property of nettle is explained once again by its inhibitory action on 5-α-reductase, the enzyme responsible for the conversion of testosterone into dihydrotestosterone (DHT). Indeed, DHT intensifies the activity of interleukin-6 (IL-6), cytokines that accelerate the transition between the growth and rest phases of hair. DHT thus more quickly induces hair follicles into the telogen phase, or hair shedding phase. By inhibiting 5-α-reductase, nettle thus protects the hair from hormonal variations or genetic predispositions leading to an increased production of DHT and consequently to hair loss.

• KHANMOHAMMAD R. & al. A Comparison of Clinical Efficacy between a Basic Shampoo with Herbal Extracts Containing Climbazole and Its Similar Sample Containing Piroctone Olamine in the Treatment of Dandruff and Seborrheic Dermatitis. Iranian Journal of Dermatology (2009).

• SEMALTY A. & al. A Comprehensive Review on Phytochemistry and Pharmacological Effects of Stinging Nettle (Urtica dioica). Current traditional medicine (2017).

• TURKOGLU M. & al. A proprietary herbal extract against hair loss in androgenetic alopecia and telogen effluvium: a placebo-controlled, single-blind, clinicalinstrumental study. Acta Dermatovenerologica (2018).