Tiny Health, a microbiome testing company, has clinched $33 million in an oversubscribed series B round.
Capital B led the round, with participation from Spero Ventures, Black Opal Ventures, Pave Health Ventures, Alumni Ventures, Gaingels and others.
The capital, which brings Tiny’s total raised to $46 million, will be used to advance research, expand provider education, scale the B2B platform and expand the patient-facing AI agent.
Alongside the funding news, Tiny announced the launch of a $5 million Microbiome Research Program to enable researchers, clinicians and scientific partners to investigate important intervention strategies in microbiome health. The idea is to help them add a microbiome layer to work they are already doing or planning using Tiny tests.
"We believe the gut microbiome represents one of the most significant and under-explored frontiers in human health," Nick Whitehead, senior principal at B Capital, said in an announcement. Whitehead will join the Tiny Health Board of Directors. He added Tiny is building “a category-defining company that can help shape the future of precision medicine and care.”
Tiny was launched in 2022, initially focusing on a microbiome test for babies and moms. "There was just a white space and nobody meeting the needs of those demographics,” Cheryl Sew Hoy, founder and CEO of Tiny Health, told Fierce Healthcare. Tiny expanded to a vaginal microbiome test, and today its adult tests have surpassed pediatric ones in volume.
The at-home gut testing kit contains a swab that requires a stool sample from soiled toilet paper. Once it’s mailed to the lab, consumers receive their results in a few weeks. These include a gut diversity score, levels of good bacteria, red flags for leaky gut and identification of common parasites or harmful bacteria.
A personalized report makes recommendations across key areas: supplements, diet and lifestyle. The report cites peer-reviewed publications and is powered by TinyAI, the company's own LLM, trained on its proprietary dataset of nearly 200,000 microbiome profiles. Tiny does not make its own supplements or recommend specific supplement brands (“We feel that may be a conflict of interest,” Sew Hoy says).
Sew Hoy stresses that the test is a wellness test, not a diagnostic one. While traditional diagnostic tests focus on identifying parasites or harmful bacteria like salmonella, Tiny’s test looks at all gut microbes, including the good ones.
“In your microbiome, there’s a lot of good bacteria that is not just there for digestive functions … there’s a gut-brain connection,” Sew Hoy explained. “We’re missing the big picture if we’re not understanding what is all in your gut.”
Tiny is seeing chronic conditions linked to a lack of good microbes, not necessarily the presence of parasites. “We used to think bad stuff causes issues, but now we’re seeing in our dataset … a big driver of a chronic condition is a lack and deficiency of the beneficial stuff,” Sew Hoy said.
The gut microbiome has emerged as a key player in immune health, metabolism and chronic disease. Seven in 10 Tiny customers are working through chronic conditions.
Sew Hoy recalled when she caught a stomach bug and her microbiome testing showed a third of her gut microbes were E. coli—the toxic kind associated with colon cancer. Around the same time, she was having other symptoms and skin flares, and was diagnosed with an autoimmune condition. Her blood inflammation markers were high. After she addressed her gut about a year and a half later, the E. coli prevalence went down significantly, as did her inflammatory biomarkers. Her other symptoms disappeared.
“It was really eye-opening,” Sew Hoy said.
Consumers have several options. They can take a test and stick with Tiny’s results and automated recommendations, they can bring the results to a doctor or they can become Tiny members to get a brief consult with a specialist.
Clinicians are generally not trained in gut health or nutrition, Sew Hoy said, and doctors had been asking Tiny for help interpreting the results. Now, the company has a dedicated clinician education arm that trains providers in its network for free. “We want to democratize access to this data,” Sew Hoy noted. Providers can apply to join Tiny’s network, get that training and be able to order tests for patients.
Tiny published an interventional randomized controlled trial in 2025 in Pediatric Allergy and Immunology. It demonstrated that targeted microbiome interventions, including health coaching, educational content and targeted probiotic and lifestyle recommendations, reduced infants’ odds of developing eczema by 83%. A second randomized controlled trial is underway. Tiny hopes to use its longitudinal microbiome dataset to explore research on IBD, menopause, GLP-1s and oncology drug response. For instance, through work with a practitioner, Tiny is seeing early signals that inflammation markers from its microbiome test may be associated with how well someone responds to GLP1s.
Tiny has over 6,000 practitioners on its platform and 47 enterprise partners, including Stanford Medicine, Fullscript, Mayo Clinic and Mass General Hospital. Its B2B platform, Powered by Tiny, grew 4x last year. Half of Tiny’s revenue comes from DTC, and while Tiny is focusing on expanding enterprise partnerships, Sew Hoy believes DTC remains a crucial access point.
Tiny tests are priced at $249 DTC, with discounts for clinicians in its network. The annual Tiny+ membership includes two tests a year for $399 (over half of Tiny customers are subscribers). The membership also includes a one-on-one call with a microbiome specialist, like a registered dietitian or clinical nurse specialist, to review results. Reimbursement is on Tiny’s roadmap, which Sew Hoy believes will only be possible with continued scientific credibility, validation and clinical evidence.