Tiny Health raised $33 million for gut testing. The eczema study is thinner than it sounds.

A six-year-old stool test company just got a lot richer

Tiny Health, the Austin startup that mails you a kit to sample your stool and sequence what is living in your gut, has raised $33 million in a Series B round led by B Capital. MedCity News and Crunchbase News both confirm the round, which brings the six-year-old company's total funding to $46 million since a $4.5 million seed in 2021. Nick Whitehead, a senior principal at B Capital, is joining the board and says the firm sees the gut microbiome as "one of the most significant and underexplored frontiers in human health."

Founder and CEO Cheryl Sew Hoy started the company in 2020 after her own son was born, when she says none of her doctors could answer her questions about infant gut bacteria. "I learned that you can course-correct if you focus on the early life of the baby," she told Crunchbase News. "If they're missing certain beneficial bacteria, it can really cause a lot of issues for the infant." That personal story now sits behind a business with close to 200,000 customers and more than 6,000 practitioners ordering its reports, including clinicians at Mayo Clinic's Executive Health and Longevity Clinic.

What $249 and a stool sample actually buy you

The test uses shotgun metagenomic sequencing, a more thorough method than the older 16S sequencing many budget gut kits rely on, to identify which bacterial species and strains show up in a sample. Tiny Health sells versions for adults, for babies and toddlers, and a separate vaginal microbiome test aimed at reproductive health. Each report translates the sequencing data into scores such as "Gut Microbiome Age" and flags bacteria that outside research has linked to conditions like eczema or digestive trouble, then recommends diet changes, specific probiotics, or a repeat test down the line.

That is a genuinely more capable approach than a lot of what passes for gut testing, and it sits inside a wider wave of gut health trends that has made microbiome talk mainstream. The sequencing technology itself is not really in dispute. What is worth scrutinizing is the leap from "we can see which bacteria are there" to the clinical claims the company is now raising money on.

The eczema study behind the pitch

Tiny Health's central evidence point is a randomized controlled trial published in Pediatric Allergy and Immunology in 2025, titled "Improving immune-related health outcomes post-cesarean birth with a gut microbiome-based program." It followed 54 healthy, full-term babies born by C-section, splitting them into a group of 25 that got Tiny Health's testing, personalized probiotics and coaching from microbiome specialists, and a control group of 29 that did not. After six months, 6% of babies in the program group had developed eczema, versus 29% in the control group, an 83% reduction in odds that now appears in the company's funding announcement and its marketing copy alike.

That is a real, statistically notable result, not an invented one. It is also a single trial, of 54 infants, designed and published by Tiny Health's own scientists rather than an independent academic lab, without any indication the parents involved were blinded to their group. Encouraging results from a company-run study are exactly the kind of finding that needs replication by outside researchers before anyone treats it as settled. Tiny Health says a second trial is underway, which is the right next step, but it has not happened yet.

A wellness test, by the company's own admission

To her credit, Sew Hoy is fairly direct about what the product is not. "We are a wellness test," she told Crunchbase News. "We're not a diagnostic ... It's very actionable, very evidence-backed." Insurance does not cover the test, and the company acknowledges it cannot tell a customer what caused their symptoms, only which bacteria are present alongside associations drawn from outside literature. That distinction matters more than it sounds. A wellness test can be genuinely useful for curiosity, or for starting a conversation with a doctor. It is a different thing from a diagnostic tool proven to change a clinical outcome, and language elsewhere in the company's own announcement, including a reference to making microbiome testing "the standard of care," blurs that line more than the CEO's own quote does.

Where the new money goes

Of the $33 million, Tiny Health says $5 million will fund a new Microbiome Research Program, opening its testing, data and bioinformatics tools to outside researchers and clinicians who apply for support, a step that could eventually produce the independent validation the eczema finding still lacks. The rest goes toward scaling "TinyAI," the company's internal analysis engine, and expanding partnerships with clinics and longevity practices. If the money genuinely buys independent replication of that eczema result, or similar trials on the adult and toddler tests, it will have been well spent. If it mostly buys faster customer growth on the back of one small trial, the underlying science will still be exactly where it is today.

Our take

Tiny Health's sequencing technology is solid, and its 83% eczema number is a real, worth-watching early signal, not marketing fiction. But it is one small, company-authored trial, not a body of independent evidence, and the CEO's own "wellness test, not diagnostic" framing is more honest than most of the language surrounding it. If you are curious about your gut, or your baby's, this is a legitimate way to look. Just do not mistake a $249 stool test for a doctor, or one 54-infant study for settled science.

Health Trend Wire holds no position in Tiny Health and was not paid for this article. This is general information, not medical or financial advice.