The Gut-Skin Axis: How Your Gut Health Affects Your Skin

What the gut-skin axis is

The gut-skin axis is the two-way connection between your gut, including the trillions of microbes that live in it, and your skin. Researchers use the term for the ways the gut can influence inflammation, oil production and healing in the skin, and for the ways stress and skin inflammation can feed back to the gut.

It's a genuine area of research, but it attracts a lot of overstatement. Most of the evidence shows that gut and skin problems tend to turn up together. Much less of it shows that fixing one will fix the other.

This article explains:

How your gut and skin communicate

Your skin and your gut lining do a similar job. Both are barriers between your body and the outside world, home to their own microbes and full of immune cells. The gut is the far larger surface: about 32 square metres in an adult, according to a 2014 estimate, against under 2 square metres of skin.

Researchers have described several routes between the two:

Where stress comes in

Doctors suspected a link long before anyone could sequence a gut microbe. In 1930, the American dermatologists John Stokes and Donald Pillsbury proposed that worry and low mood could upset the gut and its bacteria, and show up as skin inflammation. Parts of their theory have held up. Stress hormones can alter gut bacteria and gut permeability, and stress is a common trigger for flares of acne, eczema, psoriasis and rosacea. You'll see this called the gut-brain-skin axis.

Skin conditions linked to gut health

Research has connected the gut with several common skin conditions. Most of the evidence comes from observational and animal studies, so it shows a link rather than proving cause. The gut is also only one factor, alongside genetics, hormones, skin bacteria and stress.

Acne

Small studies have found lower gut bacterial diversity in people with acne, but the stronger evidence is about diet. In a 2007 Australian trial of 43 young men, a low-glycaemic-load diet cut acne lesions more than a higher-glycaemic diet over 12 weeks, although the low-glycaemic group also lost more weight. Foods that raise blood sugar quickly push up insulin and a related hormone, IGF-1, which can increase oil production. NICE doesn't recommend a specific diet for acne because the evidence is limited, and advises general healthy eating instead.

Rosacea

A Danish study of almost 50,000 people with rosacea found they were more likely than the general population to have coeliac disease, Crohn’s disease, ulcerative colitis or IBS. A small Italian trial found small intestinal bacterial overgrowth (SIBO) was more common in people with rosacea, and that clearing it improved their skin. That was one small study, though, and treating SIBO isn’t a standard rosacea therapy.

Eczema (atopic dermatitis)

Babies who go on to develop eczema tend to have less diverse gut bacteria in their first weeks of life. That has fuelled interest in probiotics during pregnancy and infancy, covered in the probiotics section below.

Psoriasis

People with psoriasis are more likely than average to develop inflammatory bowel disease, especially Crohn's disease. The two conditions share some genes and immune signalling (the IL-23 and IL-17 pathways that several biologic drugs target). Gut bacteria in people with psoriasis also differ from those in people without it, although studies haven't agreed on a consistent pattern.

How to support your gut and skin

No diet clears skin on its own, and food changes work best alongside skin treatment rather than in place of it. These habits support a healthier gut, and some have evidence for skin too.

• Eat a wide range of plants. Fibre feeds the bacteria that make SCFAs. The UK guideline is 30 g a day, and most adults fall short. In the American Gut Project, people who ate more than 30 different plant foods a week had more diverse gut bacteria than those who ate 10 or fewer.

• Add fermented foods. Try live yoghurt, kefir, sauerkraut or kimchi. In a small 10-week Stanford study, eating more fermented foods increased gut bacterial diversity and lowered several inflammatory markers.

• Cut back on fast-releasing carbs if you're prone to acne. Swap some sugary drinks, sweets and white bread for oats, pulses and whole grains.

• Eat oily fish. Salmon, mackerel and sardines provide omega-3 fats, which help regulate inflammation. The NHS suggests at least one portion of oily fish a week. Evidence for omega-3 supplements in skin conditions is limited.

• Get zinc and vitamin A from food. Both contribute to the maintenance of normal skin. Zinc comes from shellfish, meat, dairy, pulses and seeds. Vitamin A comes from eggs, dairy and oily fish, and your body makes it from the beta-carotene in carrots, sweet potato and leafy greens.

Avoid high-dose vitamin A supplements. If you're pregnant or trying to conceive, NHS advice is to avoid liver and any supplement containing vitamin A (retinol) unless your GP advises otherwise.

Sleep, stress and skincare

Poor sleep and ongoing stress affect both systems at once, so regular sleep, daylight and exercise all count (we cover the gut side in how stress, sleep and the nervous system shape your microbiome). Look after your skin from the outside too. A gentle cleanser, a moisturiser that suits you and daily sun protection support the skin's own barrier, and no amount of gut-friendly eating replaces them.

What probiotics can and can't do for skin

Probiotics get most of the attention in gut-skin marketing, but their effects are strain-specific. A result for one strain of Lactobacillus says little about another, let alone about a different product.

If you'd like to try one, choose strains that have been studied for your goal, give it two to three months, and keep using any treatment you've been prescribed. If you're pregnant or have a weakened immune system, check with your GP or midwife first.

Can a gut microbiome test help your skin?

No stool test can tell you that your gut is causing your skin problem, so be wary of any company that suggests it can. What a microbiome test can show is the state of your gut: how diverse your bacteria are, whether SCFA producers are well represented, and any signs of imbalance (dysbiosis) or inflammation. That makes it a useful baseline before you change your diet.

Stride's Optimal Biome test analyses an at-home stool sample for more than 300 gut bacteria, with diversity and SCFA scores, gut-brain markers and signs of inflammation or dysbiosis. It comes with tailored recommendations and the option to retest, and is currently available in the UK only.

Some skin problems call for blood tests through your GP as well. Acne with irregular periods or extra hair growth, for example, can point to a hormonal cause such as PMOS, previously called PCOS.

When to see a GP or dermatologist

Gut-friendly eating is worth trying alongside treatment. Acne, eczema, psoriasis and rosacea all have effective treatments, and starting early can prevent scarring and reduce flares. A pharmacist can help with mild symptoms. See your GP if you have:

Get help the same day from your GP or NHS 111 if eczema suddenly becomes very painful with clusters of blisters, or you feel feverish and unwell, as this can signal an infection called eczema herpeticum. If you have gut and skin symptoms together, mention both, as coeliac disease and inflammatory bowel disease each have recognised skin signs.

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