In 1930 two American dermatologists, John Stokes and Donald Pillsbury, published a paper with an unwieldy title and a rather daring idea. They had noticed that their patients' skin seemed to flare and settle in step with their moods and their digestion, and they proposed that the gut sat somewhere in the middle of it all, carrying messages between the mind and the skin. Medicine politely filed the idea away for the best part of a century. It has since been taken back out, dusted off and found to be remarkably close to the mark.
I come back to that paper often, because it describes something so many of the women who write to me already feel in their bones. Their skin changes when their digestion changes. It dulls during a stressful month, roughens after a run of poor sleep and takeaway dinners, and brightens again when life settles. They aren't imagining it.
A lining that decides what gets in
The inside of your small intestine is lined with a single layer of cells. Folded and ridged as it is, that lining covers around thirty square metres, roughly half a badminton court, and it is the largest surface your body presents to the outside world. Each cell is fastened to its neighbour by proteins called tight junctions.
In good health that lining is wonderfully discerning. It admits nutrients and refuses almost everything else. Stress, broken sleep, alcohol and a diet thin on protein and minerals all wear at those fastenings, and the lining grows more permeable than it ought to be. Fragments that should have stayed put slip through, the immune system grows restless, and that low-grade inflammation has a habit of surfacing elsewhere. Researchers now describe a genuine gut-skin axis, a two-way line of communication running through the immune system, and the skin is one of the places where trouble below tends to announce itself.
The consolation is that your gut lining is one of the most industrious tissues you own. It renews itself every few days, so whatever you eat this week becomes the raw material for the lining you'll have next week.
The company you keep
Living along that lining are trillions of bacteria, and they are far from idle lodgers. When they ferment the fibre you eat, they produce short-chain fatty acids such as butyrate, which feed the cells of the gut wall and help keep the immune system calm and measured. A varied, well-fed community of microbes appears to be one of the quiet foundations of skin that behaves itself.
Two studies in particular have stayed with me. At Stanford, researchers asked one group of healthy adults to eat several serves of fermented food every day for ten weeks. Their gut bacteria grew steadily more diverse, and nineteen markers of inflammation in their blood went down. In Korea, a twelve-week trial gave 110 women with dry skin either a probiotic strain of Lactobacillus plantarum or a placebo, and the women taking the probiotic finished the study with measurably more moisture in the skin of their face and hands. It was one strain, in capsule form, and the company that makes it ran the trial, so I hold it lightly. It sits comfortably alongside everything else we know, though, and L. plantarum happens to be one of the main bacteria in a properly made sauerkraut.
Where hormones come in
Your gut bacteria also take part in managing your hormones. A collection of microbes, nicknamed the estrobolome, produces enzymes that influence how much oestrogen is cleared from the body and how much is sent back into circulation. When that community is out of balance, the recycling can tip one way or the other. It is one more reason the skin can shift with the seasons of a woman's life, and one more reason looking after your gut is time well spent at any age.
What I actually eat
None of this calls for anything elaborate. These are the foods that turn up in my kitchen most weeks.
Something fermented every day. A forkful of raw sauerkraut with dinner or a small glass of kefir. Buy it from the fridge, or make your own, because shelf-stable jars have been heated and the living bacteria are long gone.
Broth and slow-cooked meat. Long, gentle cooking draws gelatine and amino acids from bones and skin into the liquid, and glutamine, the amino acid the cells of your gut lining prefer above all others, is plentiful in meat, fish, eggs and broth. A clinical trial published in the journal Gut found that glutamine reduced intestinal permeability. My slow cooked soy chicken is the easiest place to start.
Oysters, for zinc. Nothing you can eat holds more of it, and zinc helps keep those tight junctions fastened as well as being something your skin calls on every time it renews. If oysters aren't for you, dried oyster tablets or a zinc supplement taken with food will cover you. Keep to the label, because high doses taken for months quietly deplete your copper.
If you'd like to go further, I've written about why your skin goes without when your gut can't absorb nutrients and about what happens when bacteria settle in the wrong part of the gut.
And on the outside
All of that is the slow, inward work. In the meantime your skin still wants looking after from the outside, and that is the half I make for you. The Earth Tallow Balm is grass-fed Australian tallow infused with quandong, rosehip and sea buckthorn, and I press a little of it onto damp skin every night. If your skin feels thirsty, a few drops of Dew Drops underneath make a lovely pair.
Feed it from the inside, comfort it from the outside, and give it a few weeks. Skin is patient, and it tends to repay patience in kind.
Ayla, holistic health coach and founder of DAEAR
This article is general information only and is not nutritional or medical advice. Please speak with your GP or a qualified health professional before changing your diet or starting a supplement, and especially if you are pregnant, breastfeeding, taking medication or managing a health condition.
Research referred to
- Stokes JH, Pillsbury DH. The effect on the skin of emotional and nervous states. Archives of Dermatology and Syphilology. 1930;22(6):962-993.
- Helander HF, Fändriks L. Surface area of the digestive tract, revisited. Scandinavian Journal of Gastroenterology. 2014;49(6):681-689.
- Camilleri M. Leaky gut: mechanisms, measurement and clinical implications in humans. Gut. 2019;68(8):1516-1526.
- Salem I, Ramser A, Isham N, Ghannoum MA. The gut microbiome as a major regulator of the gut-skin axis. Frontiers in Microbiology. 2018;9:1459.
- O'Neill CA, Monteleone G, McLaughlin JT, Paus R. The gut-skin axis in health and disease. BioEssays. 2016;38(11):1167-1176.
- Wastyk HC et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153.
- Lee DE et al. Clinical evidence of effects of Lactobacillus plantarum HY7714 on skin aging. Journal of Microbiology and Biotechnology. 2015;25(12):2160-2168.
- Baker JM, Al-Nakkash L, Herbst-Kralovetz MM. Estrogen-gut microbiome axis: physiological and clinical implications. Maturitas. 2017;103:45-53.
- Zhou Q et al. Randomised placebo-controlled trial of dietary glutamine supplements for postinfectious irritable bowel syndrome. Gut. 2019;68(6):996-1002.
- Skrovanek S et al. Zinc and gastrointestinal disease. World Journal of Gastrointestinal Pathophysiology. 2014;5(4):496-513.