For decades, acne has been explained simply: a bacterium, Cutibacterium acnes, proliferates in a clogged pore, and it must be killed. Hence antibiotics, topical then oral, sometimes for months. This explanation is changing, and the change is coming from French academic dermatology. In a journal published by the Nantes University Hospital team, acne is no longer an overgrowth but a loss of balance among the strains of this bacterium, in a dysregulated skin ecosystem. And this ecosystem communicates with another: the gut.
This is not forum theory. Two randomized 12-week trials, one with a probiotic, the other with omega-3s, improved acne by modifying the gut microbiota. This article explains the mechanism, details the two trials, explains why the probiotic strain changes everything, and what this approach does not replace.
The paradigm shift. Acne is no longer understood as an excess of C. acnes but as a loss of diversity among its strains, in an imbalanced skin microbiome that activates innate immunity. Anti-acne antibiotics worsen this dysbiosis. The gut-skin axis. The gut microbiota regulates the immune system, and many skin diseases are accompanied by altered gut flora. Communication is bidirectional.
The two trials. A probiotic with a specific strain combined with spirulina: 50% of patients improved versus 29% with placebo at 12 weeks, double-blind. Omega-3s for 12 weeks: greater intestinal diversity, more butyrate-producing bacteria, improved severity score. The rule that matters. A result obtained with one strain does not transfer to another. The limitation. Adjunct to treatment, not replacement.
Acne is no longer an infection, it's an imbalance
The understanding of the role of Cutibacterium acnes in acne pathophysiology has recently undergone a paradigm shift: it is not the overproliferation of C. acnes, but the loss of balance between its different phylotypes, associated with dysbiosis of the skin microbiome, that leads to acne development. The loss of phylotype diversity acts as a trigger for innate immune system activation and skin inflammation. A predominance of phylotype IA1, with a more virulent profile, is observed in acne. Other bacteria, mainly Staphylococcus epidermidis, are involved and interact with C. acnes to regulate skin homeostasis. Recent studies also show that the gut microbiome is involved in acne through its interactions with the skin microbiome. Since topical and systemic antibiotics commonly used induce skin dysbiosis, this new understanding has led to a change in direction in acne treatment.
Dréno B, Dagnelie MA, Khammari A, Corvec S. Am J Clin Dermatol 2020;21(Suppl 1):18-24. DOI: 10.1007/s40257-020-00531-1
This text comes from one of the world's leading teams on acne, and it says three things that change the way we think about it. First, it's not the quantity of bacteria that matters, it's the diversity : acne-prone skin doesn't have more C. acnes than healthy skin, it has less diverse strains, with a virulent strain that dominates. Next, the ecosystem matters as much as the species : S. epidermidis, another normal skin inhabitant, participates in the balance. Finally, and this is the point that connects to this article, the intestine is involved through its interactions with the skin flora.
The authors write it in black and white: anti-acne antibiotics, both topical and oral, induce skin dysbiosis. Killing indiscriminately in an ecosystem whose problem is the loss of diversity is counterproductive in the long term. This reasoning has guided dermatology toward what the journal calls "ecobiological" treatments, targeting pathogenic strains while sparing commensal ones. This is not an argument to stop a prescribed treatment, it is an argument to discuss its duration with your dermatologist, and to take care of the flora during treatment.
How the intestine speaks to the skin
The idea of a gut-skin axis is not recent, but it has become structured since 2018 around a series of reviews. A review in Frontiers in Microbiology describes the intestinal microbiota as one of the main regulators of this axis, with effects on skin differentiation and keratinization and on cutaneous immune response. A 2021 Belgian review notes that many skin diseases are accompanied by an altered intestinal microbiome, and that the microbiome is a key regulator of the immune system, communicating with tissues and organs in a bidirectional manner.
The pathogenesis of acne is complex and multifactorial, involving genetic, metabolic, and hormonal factors in which both skin and intestinal microbiota are implicated. Numerous studies have demonstrated the bidirectionality between intestinal microbiota and cutaneous homeostasis, a communication established primarily through immune system modulation. Clinical trials with topical and oral probiotics are rare, but have shown positive results, particularly with oral probiotics, through modulation of the intestinal microbiota generating an anti-inflammatory response and restoring intestinal integrity, or through metabolic pathways involving IGF-1. Given the aggressiveness of certain standard acne treatments, probiotics should continue to be studied as alternative or adjunctive therapy.
Sánchez-Pellicer P, Navarro-Moratalla L, Núñez-Delegido E, et al. Microorganisms 2022;10(7):1303. DOI: 10.3390/microorganisms10071303
Three pathways emerge from this research. The first is immune : intestinal flora educates and regulates immune cells, which then circulate to the skin. The second is that of the intestinal barrier : a permeable wall allows bacterial fragments to pass through that sustain diffuse inflammation. The third is metabolic, via IGF-1, the growth factor that stimulates sebum and links acne to diet, as explained in our complete guide to acne and supplements.
A review published in Gut Microbes in 2022 states it straightforwardly: the mechanisms by which the intestinal microbiome affects skin health remain partially unclear. The associations are solid, the intervention trials positive, but the complete causal chain has not yet been established. It is a serious and active lead, not a fully demonstrated mechanism.
The probiotic trial, and why the strain matters
A 12-week trial was conducted in patients aged 12 to 30 years with vulgar acne. The product studied was a capsule composed of the probiotic Lacticaseibacillus rhamnosus CECT 30031 and the cyanobacterium Arthrospira platensis. Patients improved on the overall severity scale were 10 out of 34, or 29.41%, in the placebo group, versus 20 out of 40, or 50%, in the probiotic group. A significant reduction in the number of non-inflammatory lesions was observed in the probiotic group, of 18.60 lesions versus 10.54 under placebo. On the GAGS scale, 20.58% of patients under placebo showed improvement versus 42.50% under probiotic. The number of adverse events was similar in both groups.
Eguren C, Navarro-Blasco A, Corral-Forteza M, et al. Acta Derm Venereol 2024;104:adv33206. DOI: 10.2340/actadv.v104.33206
What gives this trial value is its protocol : randomized, double-blind, placebo-controlled, over twelve weeks, with two severity scales assessed by dermatologists. And it comes from the same team in Murcia that published the review on the gut-skin axis mentioned above: they formulated the hypothesis, then they tested it.
What must be read with attention is the composition. The product tested was not "a probiotic": it was a specific strain, Lacticaseibacillus rhamnosus CECT 30031, identified by its collection number, combined with spirulina. Two consequences. You cannot attribute the result to the probiotic alone; the measured effect is that of the combination. And you cannot transpose it to another strain.
In probiotics, the species is not enough: two strains of L. rhamnosus can have different effects, and a strain of another species even more so. A result is attached to an identified strain, not to a genus name on a label. This is the rule detailed in our article on how to choose a probiotic.
Let us be precise about our own product. Probiomix is based on a spore-forming strain <<<25>>> Bacillus coagulans, Bacillus coagulans LactoSpore, which has its own documentation on resistance to gastric acidity and flora support, combined with an acacia prebiotic fiber. This is not the strain from the trial, and we do not claim it reproduces the result. It follows the logic of the gut-skin axis, probiotic plus fiber, not the reproduction of a specific protocol. The spirulina from the trial, on the other hand, exists in our product as is.
The omega-3 trial, and the role of butyrate
Untreated acne patients were randomly divided into two groups, with or without omega-3 supplementation for 12 weeks. In parallel, acne-model rats received isotretinoin, omega-3, or their combination, then the colonic content of treated animals was transferred to pseudo-sterile rats. Severity was assessed by the GAGS score in patients. Omega-3 increased intestinal microbiota diversity and positively regulated its structure in both patients and rats, increased the abundance of butyrate-producing bacteria, improved patients' GAGS score, and attenuated inflammation and comedones in animals. The authors conclude that omega-3 supplementation could attenuate acne inflammation by increasing the abundance of butyrate-producing bacteria.
Huang Y, Liu F, Lai J, et al. J Dermatolog Treat 2024;35(1):2299107. DOI: 10.1080/09546634.2023.2299107
The detail that matters is butyrate. It is a short-chain fatty acid produced by certain colon bacteria when they ferment fibers. It nourishes the cells of the intestinal wall, strengthens the barrier, and exerts an anti-inflammatory action that extends beyond the intestine. In this trial, it was the bacteria that produce it that increased under omega-3, at the same time as acne improved. The flora transfer in animals, where the intestinal content from treated rats attenuated acne in recipient rats, is the strongest argument in favor of a mechanism truly passing through the intestine.
This result is consistent with the systematic review in JAMA Dermatology, which ranks omega-3s among interventions with potential benefit in acne, and with the review of dietary literature that identifies fatty acids among protective factors. The doses and forms are detailed in our omega-3 guide.
Fiber, fuel for the mechanism
If butyrate is produced by the fermentation of fiber, then fiber is the fuel for everything that precedes it. A 2024 review in Nutrients concludes that diets rich in antioxidants, fiber and plant compounds appear beneficial for skin health, by promoting a balanced microbiota and reducing inflammation, while poor dietary choices disrupt intestinal homeostasis. A review in Clinics in Dermatology adds that nutritional approaches via the gut-skin axis, oral probiotics, prebiotics and dietary modifications, can improve symptoms in certain groups.
| Lever | What it does on the axis | Level of evidence in acne |
|---|---|---|
| Probiotic with specific strain | Modifies flora, anti-inflammatory response, barrier integrity | Randomized double-blind trial, 12 weeks |
| Omega-3 EPA and DHA | Intestinal diversity, butyrate-producing bacteria | Randomized trial, 12 weeks, with animal flora transfer |
| Fiber and prebiotics | Substrate for butyrate-producing bacteria | Convergent reviews, no dedicated trial in acne |
| Low glycemic load | Less insulin and IGF-1, the metabolic pathway of the axis | Randomized trials, see the complete guide |
| Spirulina | Component of the probiotic trial formula | Effect not isolable from that of the probiotic |
This is also what justifies combining a probiotic with a prebiotic fiber rather than taking it alone: introducing bacteria without their substrate is like sowing without watering. Acacia gum, a fermentable soluble fiber and well-tolerated, is one of the classic sources of this substrate. Our microbiota guide details this mechanism.
What this approach does not replace
The Murcia review concludes that probiotics should continue to be studied as alternative or adjuvant therapy, given the aggressiveness of certain standard treatments. The systematic review in JAMA Dermatology, which evaluated 42 trials and 3,346 participants across all oral supplements, speaks of a possible role and asupportive role, emphasizing the small size of the trials. These are the right words, and this article does not exceed them.
Consult without delay in case of nodules, cysts, scars forming, acne on the back or chest, or impact on mood. Dermatological treatments have established efficacy at a level of evidence incomparably higher than that described here.
If you are taking antibiotics for your acne, the question of flora is legitimate and documented: antibiotics induce dysbiosis, the Nantes review states this. A probiotic during and after treatment should be discussed with your prescriber, who may also reconsider the duration. This is not a reason to stop a treatment on your own initiative.
The reasonable protocol
Wild fish oil, anchovies, sardines and mackerel, providing daily 640 mg of EPA and 440 mg of DHA, that is 1,200 mg of omega-3, with 4 mg of vitamin E which protects the oil from oxidation. Four capsules at meals. The category tested in the 12-week acne trial, with quantities listed on the label.
See Omega 3Medical consultation recommended in case of anticoagulant or antiplatelet treatment.
Choose what resonates most with you: the answer appears just below.
When skin and intestines protest at the same time, the gut-skin axis logic is the most direct approach. A probiotic with documented strain plus its fiber, twelve weeks, starting with one capsule to allow the digestive transit to adapt. Our bloating guide covers the other aspect.
Anti-acne antibiotics induce cutaneous dysbiosis, and oral antibiotics also affect intestinal flora. Restoring the flora after treatment is a coherent approach, to be discussed with the dermatologist who prescribed it, who may also reconsider the duration if relapse is systematic.
Without fiber, butyrate-producing bacteria have nothing to ferment, and a probiotic alone amounts to sowing without watering. Vegetables, legumes, whole fruits first, and fewer refined products, which also lowers glycemic load. The probiotic or omega-3s can come next.
Nodules, cysts and scars do not fall under the gut-skin axis, and the trial authors themselves speak of an adjuvant role. Dermatological treatments have established efficacy at another level, and every month counts for scars. Flora can accompany the treatment, not precede it.
This test provides guidance; it does not replace the advice of a healthcare professional.
Frequently asked questions
The mechanism
What is the link between the intestine and acne?
The intestinal microbiota is one of the principal regulators of the immune system, and communication between intestine and skin is bidirectional. Several reviews note that many skin diseases, including acne, are accompanied by altered intestinal flora. Proposed mechanisms involve immune response, intestinal barrier integrity, and metabolic pathways involving IGF-1. However, a 2022 review clarifies that these mechanisms remain partly to be elucidated.
Is acne caused by a bacterium?
Not in the sense it was once understood. A landmark review published by the Nantes University Hospital team describes a paradigm shift: it is no longer the overproliferation of Cutibacterium acnes that explains acne, but the loss of balance between its different strains, with a predominance of a more virulent phylotype, in the context of global skin microbiome dysbiosis. This loss of diversity triggers innate immune response and inflammation. Staphylococcus epidermidis, which interacts with C. acnes, also plays a role.
What is butyrate?
A short-chain fatty acid produced by certain colon bacteria when they ferment dietary fiber. It nourishes the cells of the intestinal wall, strengthens the barrier, and exerts an anti-inflammatory action that extends beyond the intestine. In the omega-3 trial, it was the increase in butyrate-producing bacteria that accompanied acne improvement. This is also why fiber is a lever of the gut-skin axis.
Do acne antibiotics damage the microbiome?
The Nantes University Hospital review states it explicitly: topical and systemic antibiotics commonly used against acne induce skin dysbiosis, and this new understanding has changed the direction of treatments. Oral antibiotics also act on the intestinal microbiome. This is one reason why supporting the microbiome during and after antibiotic treatment is a legitimate question to ask your dermatologist.
The trials
Do probiotics work on acne?
A randomized, double-blind, placebo-controlled trial published in 2024 followed 74 patients aged 12 to 30 years for 12 weeks with a capsule combining Lacticaseibacillus rhamnosus CECT 30031 and spirulina. An improvement in overall severity score was observed in 50% of patients on probiotics versus 29% on placebo, with a significantly greater reduction in non-inflammatory lesions. Tolerability was identical. The systematic review in JAMA Dermatology ranks probiotics among interventions with potential benefit.
Are all probiotic strains equal?
No, and this is the most important point for reading the trial. A result obtained with a specific strain, here a Lactobacillus rhamnosus identified by a collection number and combined with spirulina, does not automatically transfer to another strain or species. Other strains, such as spore-forming Bacillus , have their own documentation on intestinal microbiota and its resilience, but they were not tested in this trial. A probiotic should be chosen based on its strain and the data concerning it.
How do omega-3s work on acne?
Through the intestine, according to available evidence. A 12-week randomized trial in untreated acne patients showed that omega-3s increase intestinal microbiota diversity, enrich butyric acid-producing bacteria, and improve GAGS severity score. Butyrate is an anti-inflammatory short-chain fatty acid produced by certain intestinal bacteria from fiber. The authors conclude that omega-3s could mitigate acne inflammation through this pathway.
In practice
Do fibers play a role?
Yes, indirectly but consistently. A 2024 review concludes that diets rich in antioxidants, fiber, and plant compounds appear beneficial for skin health by promoting a balanced microbiota and reducing inflammation. Fiber is fuel for butyrate-producing bacteria. A prebiotic fiber like acacia gum combined with a probiotic follows this logic.
How long before you see an effect?
Both trials lasted 12 weeks, and that's the honest benchmark. Modifying intestinal microbiota takes weeks, and skin lesion renewal does too. Nothing should be judged before six weeks. A baseline photo in the same lighting allows you to see progressive improvement that the daily mirror doesn't show.
Can you take probiotics and omega-3s together?
Yes, they are not incompatible and work through complementary pathways on the same microbiota. But introducing both at the same time prevents knowing which one is working. The reasonable approach is to introduce one, assess it at three months, then add the other if necessary.
Does this approach replace dermatological treatment?
No. The systematic review in JAMA Dermatology speaks of a possible and adjunctive role for oral supplements. Moderate to severe acne with nodules, cysts, or scars requires a dermatologist. The 2022 review on the gut-skin axis puts it differently: given the aggressiveness of certain standard treatments, probiotics deserve to be studied as an alternative or adjunctive treatment. The key word is adjunctive.
What to remember about acne and the intestine?
That acne is an ecosystem imbalance, not a simple infection. That the intestine communicates with the skin through the immune system. That two 12-week randomized trials, one with a specific-strain probiotic combined with spirulina and omega-3s, improved acne by modifying the intestinal microbiota. That the strain matters and a result doesn't transfer from one strain to another. That fiber nourishes the mechanism. And that all this comes as a supplement to treatment, not in its place.
Glossary
- Gut-skin axis
- The set of communications between the intestinal microbiota and skin, primarily through the immune system; bidirectional.
- Dysbiosis
- Imbalance of a microbiome, due to loss of diversity or predominance of a strain; concerns skin and intestine here.
- Phylotype
- Genetic sub-group of a bacterial species; the IA1 phylotype of C. acnes is more virulent and predominates in acne.
- Strain
- Precise lineage of a probiotic species, identified by a collection number; effects are attached to the strain, not the species.
- Butyrate
- Short-chain fatty acid produced by fiber fermentation in the colon; anti-inflammatory and nourishing for the intestinal wall.
- Prebiotic
- Fermentable fiber that serves as substrate for beneficial bacteria; acacia gum is an example.
- Spore-forming
- Describes a bacterium capable of forming a resistant spore, which crosses gastric acidity before germinating in the intestine.
- IGF-1
- Insulin-like growth factor; stimulates sebum and constitutes the metabolic pathway of the gut-skin axis.
- GAGS Score
- Global Acne Grading System, severity scale weighting lesions by zone, used in both trials.
Sources
The studies cited below were identified via PubMed.
- Dréno B, Dagnelie MA, Khammari A, Corvec S. The skin microbiome: a new player in inflammatory acne. American Journal of Clinical Dermatology, 2020;21(Suppl 1):18-24. DOI
- Sánchez-Pellicer P, Navarro-Moratalla L, Núñez-Delegido E, et al. Acne, microbiome and probiotics: the gut-skin axis. Microorganisms, 2022;10(7):1303. DOI
- Eguren C, Navarro-Blasco A, Corral-Forteza M, et al. Randomized clinical trial evaluating the efficacy of an oral probiotic in acne vulgaris. Acta Dermato-Venereologica, 2024;104:adv33206. DOI
- Huang Y, Liu F, Lai J, et al. The adjuvant role of omega-3 fatty acids through upregulation of the intestinal microbiota in acne vulgaris. Journal of Dermatological Treatment, 2024;35(1):2299107. DOI
- Salem I, Ramser A, Isham N, Ghannoum MA. The intestinal microbiome as a major regulator of the gut-skin axis. Frontiers in Microbiology, 2018;9:1459. DOI
- De Pessemier B, Grine L, Debaere M, et al. Gut-skin axis: state of knowledge on the relationships between microbial dysbiosis and skin conditions. Microorganisms, 2021;9(2):353. DOI
- Mahmud MR, Akter S, Tamanna SK, et al. Impact of the gut microbiome on skin health: the gut-skin axis through therapeutics and skin diseases. Gut Microbes, 2022;14(1):2096995. DOI
- Sinha S, Lin G, Ferenczi K. The skin microbiome and the gut-skin axis. Clinics in Dermatology, 2021;39(5):829-839. DOI
- Borrego-Ruiz A, Borrego JJ. Nutritional and microbial strategies for treating acne, alopecia, and atopic dermatitis. Nutrients, 2024;16(20):3559. DOI
- Shields A, Ly S, Wafae B, et al. Safety and efficacy of oral nutraceuticals in the treatment of acne: systematic review. JAMA Dermatology, 2023;159(12):1373-1382. DOI
