The intriguing benefits of lemon hydrosol for hair?

The lemon tree is a shrub-like plant from the Rutaceae family, primarily cultivated in the Mediterranean basin. Originally, this tree grew in the Middle East. Its introduction to the West dates back to the 4th century BC, driven by Alexander the Great. During antiquity, the lemon was mainly used for its culinary properties and its anti-nausea action. Its use was then extended to other areas, notably therapeutic and cosmetic.

Thelemon hydrosol is obtained through steam distillation of the citrus fruit. However, it should not be confused with lemon essential oil, which is more active due to its higher concentration of active ingredients. Lemon hydrosol is actually water charged with a small amount of essential oil. From an organoleptic point of view, it is a colourless liquid, sometimes slightly opalescent, with a characteristic fresh and lemony smell. In terms of composition, lemon water notably contains limonene, alpha and beta-pinenes, geranial, linalool and traces of vitamin C and flavonoids. Lemon hydrosol is a natural ingredient used in the manufacture of various cosmetic products. While its effects on the skin are generally well known, it is important to highlight that lemon hydrosol also brings benefits to the hair.

Please note : one should not confuse lemon juice and lemon hydrosol. The former is highly acidic and extremely photosensitising, due to its high concentration of furocoumarins. On the other hand, lemon water is a gentle treatment suitable even for pregnant or breastfeeding women and young children.

Just like the fruit from which it is derived, lemon hydrosol contains vitamin C. This vitamin promotes the production of collagen by fibroblasts, a protein essential for the scalp. Indeed, according to some studies, collagen stimulates the synthesis of keratin, the main component of hair. This fibrous protein contributes to the structure and protection of hair fibres. It is indeed a constituent of the scales of the cuticle, the outermost layer of the hair. This layer ensures the impermeability of the hair fibre and the protection of the cortex. However, it should be noted that the studies mentioned concern vitamin C itself and not lemon water. Therefore, caution should be exercised regarding its effect on collagen production, as the only existing evidence is indirect.

The concentration of Vitamin C in lemon hydrosol is relatively low. It may be necessary to combine it with a treatment containing a higher amount of Vitamin C to achieve results.

The vitamin C found in lemon hydrosol is a recognised antioxidant . Indeed, this compound is capable of combating free radicals, reactive species that can weaken the hair follicle, and promote hair loss and split ends. Its application to the hair thus helps to protect it from certain aggressions such as exposure to UV radiation or pollution. Moreover, it slows down the appearance of grey 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 the hair fibres remains poorly understood, it seems that free radicals can trigger a chain of reactions leading to the degradation of melanin, the pigment that gives hair its colour.

Let us note once again that the low concentration of vitamin C in lemon hydrosol does not allow us to definitively determine its effectiveness.

Scalp irritations and feelings of discomfort can be alleviated through the soothing properties of lemon water. Indeed, it contains several molecules with anti-inflammatory properties. The linalool in its composition 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...), which could potentially cause inflammatory phenomena. Additionally, lemon water contains geranial. A study has shown that this molecule inhibits the activity of NLRP3, a inflammasome complex that triggers an inflammatory signalling pathway. It notably increases the synthesis of interleukin-1 (IL-1) and interleukin-4 (IL-4), pro-inflammatory cytokines. Thus, applying a lemon hydrosol to the scalp can help to alleviate itching, which also limits its flaking.

The presence of linalool in lemon hydrosol makes it an effective repellent against parasites of the scalp and hair, such as lice. Indeed, this molecule inhibits acetylcholinesterase, an enzyme found in these parasites that leads to the degradation of their acetylcholine neurotransmitter. This mechanism is the cause of the neurotoxicity of lemon hydrosol for lice. To combat these, you can use lemon water in synergy withlavender essential oil, which has recognised anti-lice properties. Apply a drop of this mixture behind each ear and massage. This treatment can be used as a preventive or corrective action.

According to some sources, lemon water is said to have matifying and purifying properties, and could help to reduce the overproduction of sebum by the sebaceous glands, which is the cause of oily hair. Indeed, it seems that the linalool present in its composition may have a sebum-absorbing effect. However, no scientific study focusing on lemon hydrosol itself has so far been able to demonstrate this property. Therefore, we cannot assert that the application of this extract has a genuine purifying action. Furthermore, the concentration of linalool in lemon water is very low and may be insufficient to induce an effect.

• SEIBERG M. Age-induced hair greying - the multiple effects of oxidative stress. International journal of cosmetic science (2013).

• BEKHIT A. & al. Keratin: dissolution, extraction and biomedical application. Biomaterials science (2017).