A prebiotic is a plant material that feeds microbes. A probiotic is the microbe. Put the two together and let them work, and what they produce is a postbiotic. In bio-fermented skincare all three are in play before the bottle is ever filled — and all three are named in a single line on the ingredient list.
Once you can see how they fit together, the back of a bottle stops being a wall of Latin and starts telling you exactly how the product was made.
What's the difference between prebiotics, probiotics and postbiotics?
All three have proper definitions, set by the International Scientific Association for Probiotics and Prebiotics in consensus statements published in 2017, 2014 and 2021 respectively.1,2,3 They were written years apart and they all end the same way — confers a health benefit on the host. What changes is the role each one plays.
| Prebiotic | Probiotic | Postbiotic | |
|---|---|---|---|
| The definition | "A substrate that is selectively utilized by host microorganisms conferring a health benefit" | "Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" | "A preparation of inanimate microorganisms and/or their components that confers a health benefit on the host" |
| Set in | 2017 | 2014 | 2021 |
| In plain terms | The food | The microbe | What the two produce together |
| In bio-fermentation | The plant material going in | The strain that ferments it | The result, which goes into the formula |
Worth knowing: all three definitions were written for food and supplements. Only the prebiotic one mentions skin — the 2017 consensus says prebiotics "can also be administered directly to other microbially colonized body sites, such as the vaginal tract and skin."1 They're also scientific consensus definitions rather than labelling rules, which is why the words get used more broadly in cosmetics than in the research.
How does bio-fermentation actually work?
You take a plant material, introduce a live culture, and let it work. What comes out is not what went in.
Step by step:
- Start with the plant material. Licorice root, papaya fruit, pineapple, aloe vera leaf juice. This is the prebiotic — the food.
- Introduce the probiotic strain. In our case, Lactobacillus. It's alive and it's hungry.
- Let them ferment together. The strain feeds on the plant material, breaking large molecules into smaller ones and synthesising compounds that weren't in the raw ingredient at all. Peptides, organic acids, enzymes.
- What that produces is the postbiotic. The transformed material, plus the spent cells and cell fragments.
- The postbiotic goes into the formula, and the formula goes into the bottle.
So the probiotic is essential to everything that follows — and it does its work before the product exists. What reaches your face is what the fermentation produced.
What is a prebiotic, exactly?
Food for microbes. In bio-fermentation, it's the plant material you give the culture to work on.
The word selectively in the formal definition is doing real work. A prebiotic isn't general nutrition — it has to be preferentially used by the organisms you actually want, rather than feeding everything indiscriminately. The same logic applies whether the microbes in question are in a fermentation tank or living on your face.
What is a probiotic, exactly?
Live microorganisms, enough of them, doing you some good.2
In bio-fermented skincare the probiotic strain is the engine of the whole process. Choosing it is a formulation decision in its own right: different strains fed the same plant material produce different compounds. Fermentation isn't one process with one outcome.
Can a skincare product contain live probiotics?
Some can, but it's unlikely, and the reason is a formulation constraint.
For a live topical probiotic, the organisms have to still be alive when the product reaches your face — through manufacture, the preservative system, a warehouse, a courier in an Australian summer, and however long the jar sits in your bathroom. Preservatives exist to kill microorganisms, because an unpreserved water-based cosmetic is a contamination risk. It can be engineered around with spore-forming organisms, waterless formulas or specialised packaging, but it's difficult.
Bio-fermentation takes a different route. Rather than asking live organisms to survive the journey, it puts them to work first and delivers what they produced. Both approaches involve probiotics. They use them at different points.
What is a postbiotic, exactly?
A preparation of inanimate microorganisms and their components3 — in other words, what the fermentation produced, and the part that actually reaches your skin.
We've gone into this properly elsewhere: what postbiotics are and what they mean for getting the most out of your skincare covers the detail, what the research supports and what it doesn't, and why a ferment isn't the same thing as a ferment filtrate.
So which one do you actually want?
All three, working in the right order — which is what a bio-fermented ingredient is.
The quality of what ends up in the bottle depends on every decision upstream. Which strain. What it was given to ferment. How long for. Whether the fermented material is kept or filtered out at the end. Two products can both say "fermented" and contain quite different things.
A product listing all three isn't automatically better than one that does a single thing properly. For sensitive skin, what's been left out usually matters as much as what's gone in — a fragranced product with three biotics in it is still a fragranced product, and your face will certainly notice.
So the useful question isn't how many of the three a product claims. It's which specific ingredients deliver them — and that's on the back of the bottle.
How do you read it on a label?
A bio-fermented ingredient names the entire chain in one line.
Take Lactobacillus/Carica Papaya fruit ferment:
| Part of the name | What it is |
|---|---|
| Lactobacillus | The probiotic — the strain that did the work |
| Carica Papaya fruit | The prebiotic — the plant material it fed on |
| ferment | The postbiotic — what the two produced together |
All three, in one ingredient. Everything before the slash is the organism; everything after it is what that organism was given to work on; and the last word tells you what you're getting.
Two more worth knowing:
| On the label | What it tells you |
|---|---|
| ...ferment filtrate | The same process, but filtered afterwards. The ISAPP definition excludes these from "postbiotic" |
| A named live strain with a CFU count | A live probiotic, intended to arrive alive. A different approach |
What we use, and why it suits sensitive skin
Our formulas are bio-fermented, which is the whole chain running before anything is bottled. Probiotic Lactobacillus strains are fermented with plant materials, and the postbiotic that it produces is what goes into the formula: Lactobacillus/Glycyrrhiza Glabra Root ferment (licorice), Lactobacillus/Carica Papaya fruit ferment, Lactobacillus/Ananas sativa fruit ferment (pineapple) and Lactobacillus/Aloe Barbadensis leaf juice ferment.
Pre-, pro- and postbiotics in every formula — each at the point in the process where it does its work.
We use ferments in every formula, not ferment filtrates. Nothing is filtered out afterwards — which matters, because the ISAPP definition excludes filtrates. The cell material left behind by the fermentation is part of what makes a postbiotic a postbiotic.3
The practical point for reactive skin is restraint. Fermentation gets more out of fewer ingredients — and fewer ingredients gives your skin the space it needs to build a stronger, more resilient barrier. And we'll never include anything from our Possibly Problematic™ list: no fragrance, no dyes, no drying alcohols, no essential oils, no silicones, no parabens, no sulphates.
Where to start
Not sure what your skin needs? The Skin Quiz takes 60 seconds and makes a recommendation based on how your skin behaves.
Or have a look at the bio-fermented skincare range — made in Australia for skin that reacts to everything, with our 30 day guarantee.
SKINPOSSIBLE™ is an Australian skincare brand formulating pre-, pro- and postbiotic products for sensitive skin, founded in Melbourne by Jade Williams.
References
- Gibson GR, Hutkins R, Sanders ME, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology. 2017;14(8):491–502. doi:10.1038/nrgastro.2017.75
- Hill C, Guarner F, Reid G, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology. 2014;11(8):506–514. doi:10.1038/nrgastro.2014.66
- Salminen S, Collado MC, Endo A, et al. The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology & Hepatology. 2021;18(9):649–667. doi:10.1038/s41575-021-00440-6
