The Gut-Skin Axis: Is Your Diet Causing Breakouts? What the Evidence Actually Says

Last updated: 28 October 2026

You are using a decent cleanser. You have invested in the serums. You are diligent with SPF. And the breakouts keep coming anyway.

If that is you, you are in good company. A large proportion of the patients who come to my clinic in Hale with congested, blemish-prone skin are doing everything right on the outside and have begun to wonder whether the problem is on the inside. Usually they have read something about the gut-skin axis, and they want to know whether it is real.

It is real. It is also one of the most over-sold ideas in skincare, and the gap between what the research shows and what Instagram claims is wide. As an NHS GP as well as an aesthetic doctor, I see both the science and the patients, so this article sets out what we actually know: which foods have evidence behind them, which do not, what the UK's own acne guideline says, and how to run a sensible experiment on yourself without giving up half your diet on the strength of a reel.

In this article:

• What is the gut-skin axis?
• Does sugar cause breakouts? The glycaemic load evidence
• Does dairy cause acne?
• Do probiotics help skin?
• What does NICE say about diet and acne?
• A twelve-week food experiment that actually tells you something
• Stress, sleep and the gut-skin-brain triangle
• When it is a GP matter, and what the clinic can treat
• Frequently asked questions

What is the gut-skin axis?

Your gut is home to trillions of bacteria and other microbes, collectively the microbiome, which help digest food, train the immune system and produce compounds that circulate around the body. The gut-skin axis is the name for the two-way conversation between that ecosystem and your skin, carried by hormones, immune signals and inflammation.

The mechanisms with the best support are not mysterious. They run through insulin and a growth hormone called IGF-1, which rise after sugary meals and certain dairy products and which increase oil production and the shedding of cells inside pores, and through inflammation, which a disrupted gut microbiome can amplify. Add stress, which alters both gut bacteria and oil production, and you have the triangle the rest of this article explores.

Pathway	What happens	How strong the evidence is
Insulin and IGF-1	High glycaemic foods and milk raise insulin and IGF-1, which increase sebum, pore blockage and androgen activity in the skin	Good: supported by randomised trials and by the biology
Inflammation	A gut microbiome low in diversity, or a diet high in refined fat and sugar, raises circulating inflammatory signals that the skin responds to	Moderate: strong in the laboratory, consistent in observational studies, few human trials
Gut permeability	Stress and poor diet are proposed to loosen the gut lining, letting bacterial fragments trigger immune activity elsewhere	Weak in humans: plausible, mostly animal data, heavily over-claimed online
Stress hormones	Cortisol shifts gut bacteria, raises oil production and slows healing	Good for the skin effects; moderate for the gut link

The gut-skin axis is real biology. The claim that a probiotic or a juice can "reset" it is marketing. The useful ground is in between, and it has numbers.

Does sugar cause breakouts? The glycaemic load evidence

This is the dietary link with the best evidence, and it is still modest.

The first randomised trial, from Australia in 2007, put 43 young men with acne on either a low glycaemic load diet (higher protein, carbohydrates from slow-release sources) or their usual carbohydrate-heavy diet for twelve weeks. Total lesion counts fell by about 22 in the low glycaemic group against 14 in the control group, alongside measurable improvements in insulin sensitivity. The catch, which the authors acknowledged, was that the low glycaemic group also lost weight, and the researchers could not separate the two effects. A 2012 Korean trial of 32 adults repeated the finding over ten weeks and added something striking: biopsies showed smaller sebaceous glands in the low glycaemic group.

Large observational studies point the same way. In the French NutriNet-Santé study of 24,452 adults, published in JAMA Dermatology in 2020, fatty and sugary foods, sugary drinks and milk were each independently associated with current acne, and a diet pattern high in fruit, vegetables and fish was associated with less of it.

The honest summary: swapping white bread, pastries, sugary drinks and sweets for oats, lentils, vegetables and whole grains is one of the few diet changes with randomised evidence for breakouts, and it happens to be good for you in every other way too. The effect is real but moderate; it will not replace treatment for established acne, and nobody should expect clear skin from a swap alone. I have written about what sugar does to skin over the longer term in Glycation: Is Sugar Ageing Your Skin?

Does dairy cause acne?

Dairy is the second best-supported link, with a twist: the evidence is entirely observational, and the pattern is odd.

The largest analysis, a 2018 meta-analysis of 14 studies covering 78,529 people aged 7 to 30, found that any dairy raised the odds of acne by about 25%, any milk by 28%, and, counter-intuitively, skimmed milk by about 32%, more than whole milk. Cheese sat on the borderline of significance. The authors noted publication bias and heterogeneity and asked for caution, and no randomised trial of dairy avoidance has ever been done.

Why would skimmed milk be worse than full-fat? The leading theory is that milk's effect comes from its proteins and growth factors, particularly whey, which drive insulin and IGF-1, rather than its fat. That fits the case reports of breakouts in people using whey protein shakes, which are the most concentrated form of exactly those proteins.

Food	What the evidence shows	My verdict
Refined carbohydrates and sugary drinks	Randomised trials of low glycaemic load diets reduced lesion counts; large observational studies agree	The change most worth making. Swap, do not starve
Skimmed and semi-skimmed milk	Consistently associated with acne in observational studies; the strongest dairy signal	Worth a six-week trial off it if breakouts are stubborn
Whey protein powder	Case series of breakouts starting with shakes and resolving on stopping	If you drink it and break out along the jaw, stop it first
Cheese and yoghurt	Weaker and inconsistent; cheese borderline in the meta-analysis	Not worth cutting unless your own experiment says otherwise
Chocolate	Small trials conflict; sugar content probably matters more than cocoa	Treat as part of the sugar picture
Oily fish and omega-3	Fair-quality trials suggest a modest anti-inflammatory benefit	Two portions a week; good for you regardless
Fruit, vegetables, fibre	Associated with less acne in large cohorts; feeds microbiome diversity	Aim for variety, around 30 different plant foods a week

One caution from the dermatologist who wrote the editorial on the JAMA study, which I share: cutting out dairy wholesale has costs, including calcium and vitamin D, so do it as a time-limited test rather than a permanent rule, and replace what you remove.

Do probiotics help skin?

This is where I have to disappoint the supplement aisle. Probiotics are the part of the gut-skin story with the most marketing and the least settled evidence.

Two meta-analyses published within a year of each other reached different conclusions. One, pooling double-blind randomised trials, found a modest reduction in inflammatory spots with oral probiotics, rated the certainty of the evidence low to moderate, and noted the trials were small and inconsistent. The other, pooling 13 studies and 1,453 participants, found no significant reduction in lesion counts, though severity scores improved a little, mostly with Lactobacillus blends taken for at least twelve weeks. A 2023 systematic review of acne supplements in JAMA Dermatology rated probiotics among the better-studied options but noted the trials were very small, and the 2024 American Academy of Dermatology guideline says there is insufficient evidence to recommend probiotics as a treatment.

So: a probiotic is safe, might help a little over three months, and might do nothing. Spend your money on the food first. A varied, plant-rich diet changes the microbiome more reliably than a capsule, and the largest microbiome study to date found that people eating more than 30 different plant foods a week had markedly more diverse gut bacteria than those eating ten or fewer.

What does NICE say about diet and acne?

Because this is the UK and I am a GP, the guideline I practise by matters. NICE's 2021 guideline on acne, developed with the British Association of Dermatologists, reviewed the dietary trials and reached a deliberately cautious conclusion:

"there is not enough evidence to support specific diets for treating acne."
NICE guideline NG198, Acne vulgaris: management, recommendation 1.3.1, 2021

The committee's reasoning is worth knowing. They accepted there was some evidence that a low glycaemic load diet may improve acne, but they could not rule out weight loss as the cause, and they judged that the effort of calculating glycaemic load was not justified by the size of the benefit. What they recommended instead was a healthy, balanced diet in line with the Eatwell Guide, and more research.

How do I reconcile that with everything above? Like this. Diet is not a treatment for acne, and nobody with real acne should be managing it with food alone when there are effective prescription treatments. But diet is a modifiable contributor to breakouts, the changes with evidence behind them are also simply good nutrition, and for the woman with mild congestion who has already tried the skincare, a structured experiment costs nothing and often helps. That is the spirit in which I discuss it.

A twelve-week food experiment that actually tells you something

The problem with "cutting out" foods on the strength of a social media post is that you change five things at once, see a result that may be coincidence (breakouts come and go with the cycle anyway), and end up on a restricted diet with no idea what helped. This is how I would do it instead.

Weeks	What to do	Why
0 Baseline	Photograph your face in the same light. Count spots. Note where you are in your cycle. Keep a plain food and skin diary for two weeks without changing anything	Breakouts fluctuate with hormones; without a baseline you cannot tell a diet effect from a good fortnight
1 to 6 Glycaemic load	Swap white bread, pastries, sweets and sugary drinks for oats, wholegrains, lentils, beans and vegetables. Keep protein at every meal. Change nothing else	The change with randomised evidence, tested on its own
6 Review	Photograph, count, compare with baseline at the same point in your cycle	One full skin cycle has passed; anything real should be visible
7 to 12 Dairy	Keep the first change. Now remove milk and whey, replace with fortified oat or soy, keep cheese and yoghurt. Add two portions of oily fish a week	Tests the dairy signal where it is strongest while protecting calcium and vitamin D
12 Decide	Compare photographs and counts across all three points. Reintroduce milk for two weeks and see whether anything changes	Reintroduction is the only way to know whether a food was really the cause

Two rules. Change one thing at a time, or you learn nothing. And eat enough: restriction and skipped meals stress the body and tend to make skin worse, not better, and if you have any history of difficulty with food, an elimination experiment is not for you.

Stress, sleep and the gut-skin-brain triangle

The gut does not only talk to the skin. It talks to the brain, and the brain talks back, which is why a stressful month so often shows on the face even when nothing about the diet has changed.

Under stress, cortisol shifts the balance of gut bacteria and raises inflammation; it also directly increases oil production and slows the skin's repair. Poor sleep removes the overnight window in which both the gut and the skin recover. And the worse the skin looks, the more stressed most people feel, which closes the loop. I have written in detail about this in How Stress Affects Your Skin, and the practical point is that a perfect diet cannot outrun four hours' sleep. If you are going to run the experiment above, run it in a month when you can also protect your sleep, or the results will not mean much.

When it is a GP matter, and what the clinic can treat

This distinction matters, and I want to be clear about it, because I wear both hats.

Your situation	Where to go	Why
Persistent, painful or deep spots, spots that scar, or breakouts affecting your mood	Your own GP, first	That is acne, a medical condition with effective prescription treatments. NICE sets out a clear pathway, and early treatment is what prevents scarring
Persistent facial redness, flushing, bumps across the cheeks and nose	Your own GP	That may be rosacea, which also has prescription treatment and which diet alone will not control
Bloating, altered bowels, pain or weight change alongside your skin	Your own GP	Gut symptoms need assessing in their own right, not treating via your face
Congestion, oiliness, occasional breakouts, uneven texture	The clinic	Medical-grade skincare with a retinoid and the right exfoliating acid, and a course of Obagi Blue Peel Radiance for congestion and tone
Dark marks left behind after spots	The clinic	Prescription pigment skincare and peels; see Post-Inflammatory Pigmentation
Scars left by past acne, once the acne is controlled	The clinic	Medical microneedling and the approaches in The Best Treatments for Acne Scars

My clinic is an aesthetic clinic. I do not diagnose or treat acne or rosacea there, and I will say so if what I see in the chair needs your GP. What I can do is improve the congestion, the texture, the marks and the scars, and talk through the dietary evidence above as the GP I also am, so that you leave with a plan that is realistic rather than restrictive.

Diet is a dial, not a switch. Turn it with the two changes that have evidence, measure, and let your GP and your skincare do the rest.

Frequently asked questions

Is the gut-skin axis real?

Yes. The gut microbiome, hormones such as insulin and IGF-1, inflammation and stress all influence the skin, and the biology is well described. What is not established is that any supplement or detox can "reset" it; the evidence-based levers are ordinary dietary ones.

Does sugar cause spots?

High glycaemic diets raise insulin and IGF-1, which increase oil production. Randomised trials of low glycaemic load diets reduced spot counts over 10 to 12 weeks, though weight loss may explain part of the effect. It is the diet change with the best evidence.

Does dairy cause acne?

Observational studies consistently link milk, especially skimmed milk, with acne, with roughly a 25 to 30% increase in odds. No randomised trial exists. A six-week trial off milk and whey, replacing them with fortified alternatives, is a reasonable test; cutting all dairy permanently is not.

Do probiotics help acne?

Possibly a little, over at least twelve weeks, and possibly not at all: the two most recent meta-analyses disagree and the trials are small. They are safe but should not be the first thing you spend money on.

What does NICE say about diet and acne?

NICE's 2021 acne guideline states there is not enough evidence to support specific diets for treating acne and recommends a healthy balanced diet instead. Diet can contribute to breakouts; it is not a treatment for acne.

How long does a diet change take to show on the skin?

At least one full skin cycle, about six weeks, and ideally twelve. Compare photographs at the same point in your menstrual cycle, because hormones move breakouts around regardless of what you eat.

Should I cut out gluten for my skin?

There is no evidence that gluten causes breakouts in people without coeliac disease or a diagnosed sensitivity. If you suspect either, that is a GP matter and should be tested properly before you remove gluten from your diet.

Can the clinic treat my acne?

No, acne and rosacea are medical conditions for your own GP, who can prescribe effective treatment. The clinic treats the cosmetic side: congestion, texture, the marks spots leave behind and, once the acne is controlled, the scars.

Further reading

• The Best Treatments for Acne Scars
• Post-Inflammatory Pigmentation: Marks After Spots
• Glycation: Is Sugar Ageing Your Skin?
• Rosacea, Redness and Flushing: What Actually Works
• Obagi Blue Peel Radiance in Hale, for congestion and uneven tone
• Medical microneedling in Hale, for the scars acne leaves behind

Next steps

Learn more about Dr Caroline Warden Clinic

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About the author

Dr Caroline Warden is an NHS GP with nearly twenty years in medicine, an independent prescriber, and holds a Level 7 postgraduate diploma in cosmetic injectables. She is the sole treating practitioner at Dr Caroline Warden Skin & Aesthetic Clinic, 2 Crown Passages, Hale, Altrincham, Cheshire. GMC number 6157708. The clinic is an aesthetic clinic and does not diagnose or treat acne, rosacea or other medical conditions; patients who need medical treatment are directed to their own GP.

References

1. National Institute for Health and Care Excellence. Acne vulgaris: management. NICE guideline NG198, June 2021, recommendation 1.3.1 and rationale on diet. Read the guideline.
2. Smith RN, Mann NJ, Braue A, Mäkeläinen H, Varigos GA. A low-glycemic-load diet improves symptoms in acne vulgaris patients: a randomized controlled trial. American Journal of Clinical Nutrition. 2007;86, pages 107 to 115. Read the companion JAAD paper.
3. Kwon HH, Yoon JY, Hong JS, et al. Clinical and histological effect of a low glycaemic load diet in treatment of acne vulgaris in Korean patients: a randomized, controlled trial. Acta Dermato-Venereologica. 2012;92, pages 241 to 246. Summary of diet trials.
4. Juhl CR, Bergholdt HKM, Miller IM, et al. Dairy intake and acne vulgaris: a systematic review and meta-analysis of 78,529 children, adolescents, and young adults. Nutrients. 2018;10(8):1049. Read the study.
5. Penso L, Touvier M, Deschasaux M, et al. Association between adult acne and dietary behaviors: findings from the NutriNet-Santé prospective cohort study. JAMA Dermatology. 2020. NHS summary and editorial commentary.
6. Tjiu JW, Lu CF. Oral probiotics in acne vulgaris: a systematic review and meta-analysis of double-blind randomized clinical trials. Medicina. 2025;61(12):2152. Read the study.
7. Julanon N, Unhapipatpong C, Wongjirattikarn R, et al. Role of probiotics in managing acne vulgaris: a systematic review and meta-analysis of clinical trials. Journal of Cutaneous Medicine and Surgery. 2026. Read the abstract.
8. Shields A, Ly S, Wafae B, et al. Safety and effectiveness of oral nutraceuticals for treating acne: a systematic review. JAMA Dermatology. 2023. Read the summary.
9. McDonald D, Hyde E, Debelius JW, et al. American Gut: an open platform for citizen science microbiome research. mSystems. 2018. Read the summary.