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A bacterium’s full name has three parts, and each one tells you something different. Most skincare labels give you one or two. Here is what each part actually carries, and why the whole name is worth asking for.
The short answer
Genus tells you the broad family. Species tells you what the organism fundamentally is and does, and it carries far more than people assume. Strain identifies one specific isolate, which is what you need when a particular effect is being claimed. Different questions are answered at different levels.
There is a slogan in this field that everything about a probiotic is strain-specific. It gets repeated a lot, including by people who should know better, and it is not quite right.
A great deal is determined at the species level. Some things genuinely do come down to the individual isolate. Knowing which is which is what lets you read a label properly.
Three parts, narrowing as you go.
Anatomy of a name
Lactiplantibacillus
plantarum
ABC-123
Genus • Species • Strain designation
Genus and species are italicised. The strain designation is not, and is usually letters and numbers assigned by whoever isolated it.
Level one
Genus
What it tells you: the broad evolutionary family. Roughly where an organism sits in the tree of life, and often a general sense of its lifestyle.
What it does not tell you: much of practical use. And genus boundaries move. In 2020 the genus Lactobacillus was split into 25 genera after whole genome analysis showed it was far too diverse to sit under one name.1 That is why Lactobacillus plantarum is now Lactiplantibacillus plantarum. Same organism, better name.
Level two
Species
What it tells you: a great deal, and more than the strain-specificity slogan suggests. Core metabolism sits here. A lactic acid bacterium produces lactic acid because of what it is, not because of which isolate it happens to be. Broad ecological role sits here. So does the bulk of the published literature, which is why there are thousands of papers on L. plantarum as a species.
Safety frameworks work at this level too. Europe’s Qualified Presumption of Safety system assesses taxonomic units, which for bacteria means species, then attaches conditions to be checked on the individual strain, such as absence of acquired antimicrobial resistance genes.2
Researchers have argued explicitly that some effects are shared across a species or even a genus rather than being unique to one isolate.3 So a species-level statement about a species-level property is a perfectly sound thing to make.
Level three
Strain
What it tells you: which specific isolate this is. Two organisms of the same species are not genetically identical, and some traits vary between them: how strongly they adhere, what they secrete, how they interact with an immune system, and anything that has been deliberately engineered.
When it becomes essential: whenever a particular effect is being claimed. A study is run on one isolate, and its findings belong to that isolate. If a brand cites research to support a specific claim, the strain in the study and the strain in the jar need to be the same one.
Once you see the three levels separately, the useful test is not “did they name the strain”. It is this:
A claim is only as good as the level of the name it rests on.
Species is enough for
“These are lactic acid bacteria and they produce lactic acid.”
“This organism has a documented safety history in this application.”
“This is what this kind of organism is and does.”
Strain is required for
“A study showed this specific effect.”
“This organism does something others of its species do not.”
Anything engineered or selected for an unusual property.
The failure mode to watch for is borrowing. A brand names a species, cites research performed on a different isolate of that species, and lets you assume the finding transfers. Sometimes it does. Often it does not, and nothing on the label tells you which.
Even when a claim only needs the species, giving the full name is better practice, for three reasons.
1. It is checkable. A named strain can be traced to a culture collection. A reader can verify that something specific and identified is in the product rather than a category.
2. It locks the supply chain. This is the one people outside manufacturing rarely think about, and I think it matters most.
3. It makes the claim auditable later. If research emerges on that organism, good or bad, it can be connected to the product. A species name makes that impossible in either direction.
Say a product lists only L. plantarum. That gives the manufacturer complete freedom over sourcing. Next production run, a different supplier, a different isolate, still perfectly entitled to the same label.
The replacement might be excellent. That is not the issue. The issue is that the customer bought a product and received a slightly different one, with nothing on the label to indicate it changed. Over time that shows up as variation between jars, and the person using it has no way to understand why.
A named strain closes that door. It commits the manufacturer to one organism from one source, which means the thing you buy next year is the thing you bought this year.
For the person buying
You know what you are getting, and you know it will be the same next time. Consistency between batches becomes something you can expect rather than hope for.
For the person making it
A fixed specification to purchase and manufacture against. It removes an easy shortcut, which is exactly why it is worth committing to publicly.
Naming the strain is a constraint a brand accepts voluntarily. That is what makes it meaningful. Anyone can write a species name. Publishing a strain designation means giving up the option to quietly change what is in the jar.
Here is something that trips up almost everyone, including people who work in this industry.
The ingredient list on a cosmetic is not written in ordinary language. It uses a controlled vocabulary called INCI, maintained by an international nomenclature committee, and US labelling rules give preference to those names.4 Every ingredient has to appear under its assigned INCI name or not at all.
INCI has no mechanism for strain designations. None exists for any microorganism. So a brand that knows exactly which isolate it uses, and would like to tell you, still cannot put it in the ingredient list. That is a limitation of the naming system, not a decision the brand made.
The part that matters
The ingredient list is one part of a label. The rest of it can carry any information that is truthful and not misleading.
Nothing prevents a company printing the strain on the carton, the back panel, or the product page. So when a brand is silent about which isolate it uses, that silence is a choice, not a constraint.
Which changes where you should be looking. An ingredient list reading only Lactobacillus tells you nothing about how careful the brand is, because that may be all the system permits. Read everything else instead. If the strain appears nowhere on the pack, nowhere on the website, and nowhere in the answer you get when you email and ask, that is the signal.
In plain terms
Species tells you what kind of thing it is. Strain tells you which one. For most of what you would want to know about a probiotic, the species is doing the work. For anything specific, the strain is the only honest answer.
✓ An organism identified at least to species, written properly and consistently.
✓ A claim pitched at the level the name supports, rather than reaching beyond it.
✓ If research is cited for a specific effect, that it was run on the organism in the product.
✓ The strain named somewhere on the pack or the website, since the ingredient list is not permitted to carry it.
Key takeaways
✓ A full name has three parts: genus, species, strain. Each carries different information.
✓ Species carries more than the strain-specificity slogan suggests: core metabolism, ecological role, most of the literature, and the safety framework.
✓ Strain matters when a specific effect is claimed, or when an organism has been engineered or selected for something unusual.
✓ Genus names are revisable. Lactobacillus became 25 genera in 2020.
✓ Naming the strain also locks the supply chain. Without it, a maker can change isolate between runs and the label stays true, while the product quietly varies.
✓ The ingredient list cannot carry a strain designation, because INCI has no mechanism for one. The rest of the label can. Silence there is a choice.
✓ The test is not “did they name the strain”. It is whether the claim matches the level of the name.
References
Links go to the peer-reviewed record. You are welcome to check my work.
1. Zheng J, Wittouck S, Salvetti E, et al. A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae. Int J Syst Evol Microbiol. 2020;70(4):2782–2858. PubMed 32293557
2. European Food Safety Authority. Qualified presumption of safety (QPS) assessment. QPS applies to taxonomic units, which for bacteria are species, with qualifications tested at strain or product level. efsa.europa.eu
3. Sanders ME, Benson A, Lebeer S, Merenstein DJ, Klaenhammer TR. Shared mechanisms among probiotic taxa: implications for general probiotic claims. Curr Opin Biotechnol. 2018;49:207–216. PubMed 29128720
4. US Code of Federal Regulations, 21 CFR 701.3, Designation of ingredients. Ingredient names are taken from the International Cosmetic Ingredient Dictionary and Handbook, published by the Personal Care Products Council, with a defined order of alternatives where no INCI name exists. eCFR • FDA
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About the author
Dr. Farzaneh Rezaei, PhD, Microbial Formulation Scientist
Founder of Fafabiotic, with two decades developing microbial technologies. She writes Ask the Scientist to explain the science behind probiotic skincare without the marketing layer.
Educational content only. This article is not medical advice and is not intended to diagnose, treat, cure or prevent any disease.
