Three years ago, Ms Danielle Fleming, a real estate agent in Hoboken, New Jersey, started suffering persistent acne around her jawline. She had "ugly, weird pimples", she said.
After switching detergents, hair spray and anything else she could think of, she went to a dermatologist to ask about a prescription for Accutane or maybe a laser treatment. What she left with was a diet.
It took Ms Fleming, 43, two years to adhere to the gut-changing diet suggested by Dr Whitney Bowe, a dermatologist in New York.
The diet, set forth in Dr Bowe's book The Beauty Of Dirty Skin, is essentially low-glycemic index foods along with bacteria-rich fermented ones. It is meant to alter the trillions-strong population of gastrointestinal micro-organisms, quelling inflammation, including skin-related outbreaks.
But Ms Fleming, a self-confessed sugar addict, was reluctant to give up her artificially sweetened yogurt and her bulk candy store habit, and hoped that following bits of the diet inconsistently would be enough.
Finally, she gave in.
"I haven't had a breakout since," she said. "And people ask me all the time what I'm doing to my skin."
Fixing the gut microbiome has been linked to a wide range of health benefits (it may, according to some studies, help lower incidence of cancer, strokes and obesity), and much of skin care, the beauty category most affected by wellness trends, is now focused on the gut as the secret to complexion perfection.
So comes a wave of designer probiotic pills and powders - stylishly packaged, with names like Glow and Inner Beauty - that suggest they can do a lot of the heavy lifting of that gut-fixing for you.
Consider this: The Beauty Chef, an Australian firm founded by a former beauty editor, offers seven probiotic-laced products that occasionally sell out on Net-a-Porter and Goop. This year, make-up guru Bobbi Brown introduced no-water-needed lemon-flavoured probiotic "pixie sticks" in her Evolution 18 wellness line.
Ms Rose-Marie Swift, the make-up artist who is known for creating glowing skin for models and celebrities such as Kate Bosworth, Gisele Bundchen and Miranda Kerr, recently introduced probiotic supplements under her RMS beauty brand, inspired partly by her relative lack of success getting models to eat foods with live cultures.
"You'd get these beautiful models, and they'd have really bad skin," said Ms Swift, who, because of a previous illness, has been preaching probiotics and safer cosmetics for years before either was trendy. "I'd tell them to eat fermented foods, but nobody does."
Unfortunately, cleaning up your gut (and your skin) is not as simple as swallowing a probiotic. Not yet, anyway.
CAN I JUST SWALLOW A SUPPLEMENT?
There are small studies associating certain strains of bacteria with acne reduction, skin hydration and elasticity. For example, one called lactobacillus casei subsp. casei 327 (or L. K-1 for short) seems to improve the skin barrier and reduce flakiness, according to a Japanese study last year. Another strain, lactobacillus rhamnosus SP1, has been linked to a reduction in adult acne, reported a 2016 study.
So why can't you simply swallow the strains in pill form and watch them automatically take effect?
First, it is not even well-established that a strong stomach, bacterially speaking, is the secret to clear skin. We do not know precisely what the mechanistic connections are between the gut microbiome and the skin, said Dr Justin Sonnenburg, an associate professor of microbiology and immunology at Stanford University School of Medicine, who studies gut microbiota.
It is certainly true that what happens in the gut is not confined to the gut, he said - that it is part of the integrated system that is you. Your gastrointestinal micro-organisms affect metabolism, immune response, stress. Change something in the gut microbiome - diet is one of the most powerful levers for that - and the effects ripple outward, potentially to the skin.
But there are not any good studies that assess in a systematic, controlled way whether changing the gut microbiome influences skin health, Dr Sonnenburg said. It is a further leap to say you can take a probiotic that will have an impact on your gut microbial community in a way that then changes your skin health.
Dr Yasmine Belkaid, director of the National Institute of Allergy and Infectious Disease's microbiome programme, said what these companies are doing is a logical next step - the gut microbiota is, after all, able to influence peripheral organs - but that "much more science" is needed to get there.
One problem with the current probiotics is that everyone's gut microbiome is different. Add to that the variations in each person's immune system and skin microbiome, and what it means is that whether a given probiotic will flourish - and then have an effect - is a bit of a lottery.
A small 2016 study published in the journal Cell Host & Microbe found that when a probiotic was administered orally, it persisted only in about a third of participants. (The study did not monitor health effects, only whether the bacteria took up residence.)
THE TRIUMPH OF THE UNSEXY DIET
Even if science eventually finds a strong causal connection between the microbiome and glowing skin, probiotics are not likely to be a one-stop solution.
"Supplementation by itself isn't going to be enough," Dr Bowe said. "If you just take a probiotic supplement, it's going to pass through if it doesn't have the right milieu to take hold and survive." She recommends probiotics but only in conjunction with eating right.
Dr Sonnenburg thinks it is more likely that skin solutions will eventually go the precision health route.
You would be classified as one of, say, 12 types, with each type being given different probiotics, different dosages and different mixtures combined with a different diet to enforce a certain resident bacteria community composition.
"What I would probably bet on is that it would be a mixture of probiotic and diet, or even just diet alone, that will be a much more powerful lever for impacting skin," he said. "But I've been wrong before."
The best way so far to improve your skin from within seems to be the unsexy old one of lasting diet change, mostly of the sort already linked with other health benefits: whole foods, limited saturated fat, minimal refined sugar.
And it is here that the current crop of probiotic supplements may be most effective, as a kind of gateway drug for diet overhaul.