Postbiotics explained: what they are and why they are showing up in skincare and supplements

You have almost certainly seen "probiotics" on a yoghurt and "prebiotics" on a fibre supplement. "Postbiotics" is the newest member of the family, and it is suddenly everywhere — on serums, moisturisers, infant formulas and capsules. It is also the most misunderstood, partly because the marketing arrived before a clear definition did. This page sets out, in plain language, what a postbiotic actually is, how it differs from its better-known relatives, and how honest the science can be about it so far.

This explainer sits inside our wider look at skin and vitality from within, which is itself one branch of the bigger question, why am I always tired? If you are curious why a gut-microbiome idea keeps turning up in skincare aisles, the related read on the gut–skin axis is the natural companion to this one.

What exactly is a postbiotic?

A postbiotic is a preparation made from microorganisms that have been deliberately inactivated — killed — together with, or made up of, their cell components, and shown in research to confer a health benefit. The defining feature is that the microbes are no longer alive. This is the formal meaning agreed by an international scientific panel, not a marketing term.

In 2021 the International Scientific Association for Probiotics and Prebiotics (ISAPP) published a consensus statement defining a postbiotic as "a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host". The panel deliberately chose the word "inanimate" — meaning without life — to make clear the microbes were once alive but have been killed, usually by heat, pressure or other controlled processing. A follow-up FAQ from the same group explained that the definition requires "a deliberate step" to inactivate the living microbes, which separates a true postbiotic from a probiotic that simply died on the shelf.

Two boundaries matter. First, a postbiotic does not have to come from a probiotic strain — any well-characterised microbe can qualify if the inactivated preparation shows a benefit. Second, a single purified molecule on its own is not a postbiotic: the same FAQ notes that isolated, purified metabolites fall outside the definition, partly so that a microbe-derived molecule and an identical synthetic one are not treated differently. So "postbiotic" points to the inactivated cells and the components that travel with them — not to one tidy active ingredient.

What is the difference between probiotics, prebiotics and postbiotics?

The three differ by what is actually in the preparation. Probiotics are live microbes given in adequate amounts; prebiotics are a food substrate your own microbes feed on; postbiotics are inactivated microbes and/or their components. In short: the live bug, the bug's food, and the deliberately killed bug — three different things often confused for one another.

Each has its own consensus definition from the same scientific body. Probiotics are defined as live microorganisms that, in adequate amounts, confer a health benefit. A prebiotic, in ISAPP's 2017 statement, is "a substrate that is selectively utilized by host microorganisms conferring a health benefit" — essentially certain fibres and compounds your beneficial microbes use as fuel. Postbiotics, as above, are the inanimate preparation. The table below lays the three side by side.

What this tends to mean in practice: because postbiotics are non-living, they are generally easier to keep stable — they do not need to survive storage or your stomach to "work" the way a live probiotic theoretically must. That stability is a large part of why formulators find them attractive for skincare and shelf-stable products. It is a manufacturing advantage; it is not, by itself, proof that any given postbiotic does more for you than the alternatives.

Why are postbiotics showing up in skincare?

Postbiotics appear in skincare because they are stable, non-living, and the idea of supporting the skin's own microbial community has become popular — and because a handful of small clinical studies on specific preparations have reported measurable changes in skin barrier markers. The interest is real; the evidence base is genuinely young.

One example often cited is a small clinical study of a postbiotic derived from the skin microbe Epidermidibacterium keratini (EPI-7). In a randomised, double-blind study of 55 healthy women over three weeks, the postbiotic-containing product was associated with greater improvements than the control in skin hydration, water-loss (a barrier marker), elasticity and dermal density, with no adverse effects reported over the period. A broader review of microbiome-based skincare describes postbiotics as a promising route for supporting skin barrier function, while being candid that many of the underlying studies are small and short.

It is worth keeping the framing honest. A single small, short, manufacturer-relevant study is a starting point, not a verdict — it shows a measurable change under specific conditions, not that every product labelled "postbiotic" supports skin the same way. Reviews in this space repeatedly note small sample sizes and a shortage of large, independent trials. Postbiotics in skincare are an interesting, plausible idea with early support, which is a very different thing from an established one.

What about postbiotics in supplements and infant formula?

Beyond skincare, postbiotics turn up in capsules, drinks and infant formulas, usually as heat-treated bacterial cultures. Some controlled studies report effects on markers of gut and immune function, but reviewers consistently describe the overall evidence as limited and call for larger, better-designed trials before drawing firm conclusions.

In infant nutrition, a systematic review and meta-analysis of postbiotics added to infant formula pooled nine randomised trials with about 2,065 participants and found an increase in stool secretory IgA (an immune marker) — but rated the certainty of that evidence as very low, and found no significant effect on most safety outcomes. Separately, a systematic review of postbiotics for common infections in children concluded that there is limited evidence to recommend specific postbiotics across seven trials, calling for further study. The throughline is consistency, not enthusiasm: some signals, low certainty, more research needed.

None of this is a reason to dismiss postbiotics, nor to oversell them. It is a reason to treat "contains postbiotics" as a description of an ingredient type, not a promise of a result. As with the rest of the microbiome story, the foundations — a varied, fibre-rich diet, enough sleep, and looking after the basics — remain far better established than any single biotic, a theme we return to across skin and vitality from within.

So the short version stays simple: a postbiotic is a deliberately inactivated microbe preparation with a real, recent scientific definition, distinct from the live probiotic and the prebiotic that feeds it. The early human evidence is promising in places and thin in others, and most of the loudest claims come from people selling it. Whether a postbiotic is relevant to your skin or gut depends on you — which is exactly the kind of thing worth talking through rather than guessing.

Frequently asked questions