The gut-skin axis: what your skin is trying to tell you

Your skin is a report card for what's happening inside you, and a lot of the grades come from your gut.

The gut-skin axis exists because your gut and your skin are in constant conversation. They share the same origin as you develop, they answer to the same immune system, and they respond to the same inflammatory signals. So when something is off in your gut, the messages it sends travel through your bloodstream, and your skin reads them. That's why, as a dermatologist, I think of your skin as a report card. It's reporting on what's going on inside.

I've been a board-certified dermatologist for more than 25 years, and I still prescribe creams. The skin is the one organ where you can put the medicine right on the cells that need it. But in a recent class I asked a different question: not what to put on your skin, but what your skin is trying to tell you. This is for anyone who has tried product after product and wondered whether the answer lies deeper.

Your skin is a report card, not just a surface

My father was a family doctor who did a lot of rheumatology. He could look at the pattern of inflammation in someone's hands and tell you an enormous amount about the health of the whole body. When I do a skin exam today, I still spend a lot of time on the hands, because he taught me to look for patterns.

The skin isn't alone in this. Ophthalmologists see the whole body in the eye, and masters of Chinese medicine read it in the pulse. I think of it like a hologram. Drop a hologram of a butterfly, and it breaks in two, and each piece still shows the whole butterfly. The whole is reflected in the part. Your skin is one of those parts, and it's the one you look at in the mirror every morning.

Two barriers, one immune system: why your gut and skin talk

Here's the simple split I use. You have two big surfaces that face the outside world. One is your skin. The other is the lining of your gut. It feels internal, but your gut is basically a tube that runs through you, open to the outside at both ends. What you swallow is, technically, still outside your body until it crosses that lining.

Both surfaces are barriers, and both are patrolled by the same immune system, so they end up in the same conversation. The natural bacteria in your gut make short-chain fatty acids that travel through the bloodstream as messengers. Your gut releases neurotransmitters. And when the gut is unsettled, it sends out inflammatory messengers called cytokines. When those reach the skin, the skin reacts. A 2022 review describes the same picture: when the relationship between the gut bacteria and the immune system is disturbed, the effects can show up on the skin, though the exact mechanisms are still being worked out (Mahmud et al., 2022).

Your skin has its own bacteria, too, different under your arms than on your face. Remarkably, the messages coming from your gut influence those communities as well. You can work on the skin alone, but you'd be ignoring the loudest voice in the room.

When the gut drowns out the signal

In my practice, sometimes a person is using exactly the right topical and the skin still isn't responding. The way I explain it, the cream is sending a good signal, but it's being drowned out by the noise coming from the gut.

When I hear that, I ask about a few gut patterns. One is dysbiosis, which basically means the bacteria in your gut aren't in the right ratio. People often notice sugar cravings, bloating, or irregular digestion. Another is increased intestinal permeability, what people call leaky gut, where the lining lets bacterial products slip into the bloodstream, and the body has to mount a response. Some people feel that as fatigue after eating, and some describe skin that seems to react to everything. A third is low butyrate, the fuel of the gut lining, which I wrote up in how butyrate keeps your gut barrier sealed. The fourth is stress.

The gut-brain-skin triangle: stress hits from both sides

When you're under pressure, cortisol rises. That's fine in the morning, when cortisol is supposed to wake you up. The trouble comes when it's triggered at other times of day, over and over.

That stress reaction does two things at once. It increases gut permeability, and it can turn up the oil glands in your skin, which changes which bacteria on your skin thrive. So stress reaches the skin from two directions: through the gut, and directly. That's the reason some people's skin seems to flare whenever life gets heavy.

The gut part of this has been measured in people. In a small study from Belgium, healthy volunteers who had to give a public speech showed a measurable rise in gut permeability, and the effect showed up only in the people whose cortisol actually went up (Vanuytsel et al., 2014). It was a short-term study in a few dozen people, so I hold it loosely, but a stressful moment can loosen the lining.

Physical stress counts too, even exercising too hard. That's why I put managing stress at the front. When you're chronically stressed, your gut essentially opens up, and that puts everything else behind the eight ball.

Your gut runs your collagen supply chain.

Your gut doesn't make collagen. Cells in your skin called fibroblasts do. But your gut decides whether those fibroblasts have what they need.

Think of it as a supply chain. To build collagen, fibroblasts need raw materials: amino acids like glycine and proline, plus vitamin C, zinc, and copper. All of it is absorbed through your gut. If the gut isn't absorbing well, collagen production slows. On top of that, chronic gut-driven inflammation activates enzymes that break down existing collagen faster than it can be replaced.

Vitamin C deserves its own mention. Many animals make their own, but your body can't, and collagen depends on it. Normal skin holds high concentrations of vitamin C, where it supports collagen formation and helps protect against damage from UV light (Pullar et al., 2017).

Then there's sugar. When blood sugar runs high, the sugar binds to the collagen in your skin, a process called glycation. The collagen becomes stiffer and less elastic, and skin can look dull and lined earlier than you'd expect. I go deeper on that in why your blood sugar spikes.

For raw materials from food, I love gelatin. It's essentially a form of collagen, and it's one of the richest food sources of glycine, proline, and hydroxyproline, the three amino acids that form collagen's backbone. Traditional Jewish chicken soup was made with the necks and the feet, and that's why it turns solid when it cools. That jelly is the gelatin. At home I make my own with plain, high-quality gelatin and a little pomegranate juice, not the boxed, artificially flavored kind.

Go over these with your own doctor, and if one comes back off, find out why. I've had patients who were the picture of health with an elevated hs-CRP. For one, the number only came back into the normal range once they started routine dental care. Inflammation in the gums was enough to register across the whole body. That's the hologram again.

Where I start: the foundations

Acne, eczema, psoriasis, and rosacea are medical conditions, and they deserve a proper exam and a plan from a dermatologist. I'm not going to pretend a food takes care of them. What I can give you is the foundation I want everyone standing on, because it supports normal gut and skin function, whatever else is going on.

• Manage stress first. Breath, stillness, a few quiet minutes with your imagination, repeated daily.
• A little fermented food every day. Kefir, kimchi, or sauerkraut. Not every meal, just daily. I sort out the terms in prebiotic vs. probiotic.
• A wide variety of plant fibers. Different vegetables feed different bacteria in your gut.
• Omega-3s from food. Low-mercury fish like salmon, sardines, and mackerel. Your index tells you where your current diet puts you.
• Fewer ultra-processed foods. This one applies to everyone.
• Use your muscles. Working muscles release chemical messengers with anti-inflammatory effects, and those messages reach your skin too.
• Protect your sleep. Your skin does its rest-and-recharge work at night.

None of this means giving up on skin care. There are stellar topicals, and some of the innovations coming out of Korea are really exciting. But the glow you're trying to buy is built within, and the two work together.

Questions I get about this

If I work on my gut, will my skin condition go away?

I can't promise that. Skin conditions need a diagnosis and care from a dermatologist. What I can tell you is that the skin reflects what's happening inside, so in my practice I don't look at it in isolation. I ask about digestion, stress, and sleep, and I look at those four numbers. Your skin is one grade on the report card, and it's worth knowing the other subjects.

Is rosacea connected to the gut?

There's an association. A nationwide Danish study compared nearly 50,000 people with rosacea to the general population and found that people with rosacea were more likely to also have certain digestive conditions, including celiac disease, Crohn's disease, and irritable bowel syndrome (Egeberg et al., 2017). That's an observational study, so it can't tell us which causes which, and the authors say plainly that the link is unknown. I expect dermatologists to ask about the gut much more often. If you have rosacea and digestive symptoms, tell your doctor about both.

Should I take collagen?

For years I resisted it. It seemed too perfect that eating collagen would help your body make collagen. The early studies, many from Japan, made me take it more seriously. But I'd start with the supply chain: gelatin or real bone broth, vitamin C from food, and a gut that absorbs them well.

References

1. Mahmud MR, et al. Impact of gut microbiome on skin health: gut-skin axis observed through the lenses of therapeutics and skin diseases. Gut Microbes. 2022. PubMed
2. Vanuytsel T, et al. Psychological stress and corticotropin-releasing hormone increase intestinal permeability in humans by a mast cell-dependent mechanism. Gut. 2014. PubMed
3. Pullar JM, Carr AC, Vissers MCM. The roles of vitamin C in skin health. Nutrients. 2017. PubMed
4. Egeberg A, et al. Rosacea and gastrointestinal disorders: a population-based cohort study. British Journal of Dermatology. 2017. PubMed