Microbiome Food / Oligosaccharides
Non-living ingredients — typically sugars, oligosaccharides and polyols — that act as selective food for the beneficial microbes living on your skin, helping a balanced microbiome flourish. The everyday cosmetic prebiotics are inulin, alpha-glucan oligosaccharide, fructooligosaccharides (FOS) and xylitol; you'll also meet marketing shorthand like "prebiotic thermal water" in the La Roche-Posay Toleriane range and "prebiotic oat" in Aveeno Calm+Restore. Prebiotics are the first leg of the microbiome trio: they feed the flora you already have, whereas probiotics add live cultures and postbiotics supply the by-products microbes leave behind.
Like postbiotics, prebiotics are a class rather than a single measured active. Oligosaccharides such as inulin and FOS do their job at fractions of a percent, and thermal-water or oat-derived prebiotics are woven into the base — so INCI position tells you little. What matters is the specific, characterised prebiotic and the formula's microbiome intent, not a percentage; standardisation between brands is poor, so judge the ingredient, not its rank.
Layer like any hydrating or soothing step — after cleansing, before heavier creams, AM and/or PM. Prebiotics are among the gentlest microbiome actives and pair comfortably with niacinamide, hyaluronic acid and barrier lipids, with no meaningful conflicts against actives like retinoids or acids. They suit sensitive, reactive and barrier-compromised skin, which is why they cluster in soothing ranges like La Roche-Posay Toleriane and Aveeno Calm+Restore. Most prebiotic sugars are exceptionally well tolerated, so they are an easy first microbiome ingredient to trial.
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