Inulin: everything you need to know about this prebiotic.

Inulin is a fibre prebiotic that was named after the botanical genus Inula, including elecampane (Inula helenium), from which it was first extracted in the early 19th century . It is also found in other plants, including chicory, Jerusalem artichoke, and dahlia.

Theinulin is traditionally extracted with hot water, but it is also possible to utilise enzymes and ultrasound to facilitate the release of the compound from plant cells through hydrolysis or by creating turbulence, respectively. Chemically, it is a linear polysaccharide composed of glucose and fructose units.

Probiotic bacteria utilise inulin as a prebiotic food source. Its use is common as a food ingredient due to its thickening and sweetening properties, as well as in certain nutritional supplements, and finally in cosmetics under the INCI name "Inulin". Indeed, it is sometimes used because of its moisturising and softening virtues on the skin.

Theinulin possesses interesting skin properties. It is found in skincare products, such as cleansers, creams, serums, and masks. The concentrations of inulin in these cosmetics are generally between 0.5 and 3%. It is also consumed orally, in dietary supplements in the form of powder or granules to be diluted.

• Inulin rebalances the skin microbiota.

  Indeed, studies have shown that its topical use prevents the proliferation of pathogens Escherichia coli, Corynebacterium striatum, Staphylococcus aureus, Pseudomonas stutzeri and Sphingomonas anadarae, while promoting the proliferation of "good bacteria" such as Staphylococcus equorum, Streptococcus mitis, Halomonas desiderata and Staphylococcus epidermidis.

  It has been proven that inulin enriches the sugar degradation pathways of "good" bacteria. Therefore, inulin would act on the skin microbiota by impacting the bacterial metabolism. As a result, the risks of skin conditions associated with pathogenic bacteria are reduced, and the skin's microbiota becomes "healthy" again.

• Inulin promotes skin hydration.

  Inulin appears to promote skin hydration when applied topically. Firstly, the bacteria it encourages (H. desiderata and S. mitis) are positively correlated with skin hydration, and the bacteria it reduces (P. stutzeri and S. anadarae) are negatively correlated with skin hydration.

  Furthermore, inulin is used by bacteria to synthesise carbonic acids, such as lactic acid. It plays a crucial role in controlling skin hydration and also promotes skin regeneration. Thus, the skin maintains a good water content, appearing plumper and less dry.

• Inulin and its antioxidant properties.

  Inulin can act as a free radical scavenger, produced in response to oxidative stress (UV radiation, pollution, tobacco, etc.), which negatively impacts DNA and dermal fibres such as collagen and elastin. As a result, inulin can prevent the acceleration of skin ageing and improve skin elasticity.

• Inulin reduces skin inflammation when consumed orally.

  A recent study has demonstrated that a diet rich in inulin can reduce the levels of pro-inflammatory mediators in the context of psoriasis. Therefore, consuming inulin could potentially reduce the symptoms associated with inflammatory skin diseases. Indeed, the intake of inulin leads to an increase in propionate levels.

  Indeed, it is known that the use of oral propionate can reduce inflammatory infiltrates and mRNA levels of inflammatory cells in dermatitis. The symptoms of dermatitis and other inflammatory skin diseases are improved by dietary inulin supplementation, and it is therefore attributed with anti-inflammatory effects when taken orally.

• Inulin could potentially prevent or reduce grey hair.

  There is no scientific evidence of the effect of inulin on hair. However, it is possible to hypothesize potential benefits, particularly in relation to the antioxidant properties of inulin.

  Studies have shown that photo-aggravation of hair oxidation leads to a drying out of the hair fibre, linked to lipid oxidation. Indeed, by preserving the integrity of the hair proteins from the impact of the sun, the hair pigments can themselves be discoloured, leading to grey hair.

  Thus, we can hypothesise that inulin, through its antioxidant effect against lipid peroxidation, could contribute to preventing or reducing hair greying by preserving melanin pigments. However, let's remember that these are only hypotheses.

Theinulin generally has a positive safety profile. It can be used without risk of skin irritation and without any known risk of interaction with other components. However, data is insufficient regarding its safety for the skin for pregnant and breastfeeding women, as well as for children. If you are in a similar situation, it is recommended to consult your doctor before using a cosmetic product containing inulin.

However, like any ingredient, there can be side effects, such as allergic reactions, which are nonetheless rare. Furthermore, these reactions can be primarily attributed to the skincare products that include it. Performing a skin test for each new product is therefore recommended as a precaution to assess any potential skin reactions. If an adverse effect occurs, it is advised to discontinue the use of the treatment and inform your doctor as soon as possible.

• CUI S. W. & al. CHAPTER 13 - Dietary fiber: fulfilling the promise of added-value formulations. Modern Biopolymer Science (2009).

• HETLAND R. B. Risk assessment of "other substances" – Inulin. Vitenskapskomiteen for mattrygghet (2016).

• TRIPODO G. & alInulin as a multifaceted (active) substance and its chemical functionalization: From plant extraction to applications in pharmacy, cosmetics and food. European Journal of Pharmaceutics and Biopharmaceutics (2019).

• SZMUC E. & al. Inulin as an effectiveness and safe ingredient in cosmetics. Polish Journal of Chemical Technology (2019).

• BOYD T. & al. The prebiotic effect of triple biotic technology on skin health. Journal of Cosmetics, Dermatological Sciences and Applications (2021).

• BOYD T. & al. Multi-omic approach to decipher the impact of skincare products with pre/postbiotics on skin microbiome and metabolome. Frontiers in Medicine (2023).