Maternal Gut Microbiome and Baby Eczema: 2026 Study Findings

A pregnant person’s gut bacteria can predict whether their baby develops eczema in the first year of life. That is the headline finding of an August 2026 Nature study of 714 Dutch mother–infant pairs, the largest longitudinal look at how the maternal microbiome shapes a newborn’s. Mothers whose infants later developed eczema had lower gut microbial diversity during pregnancy, and the association held after controlling for smoking and family history of allergy.

Key takeaways

• A 2026 Nature study sequenced 4,526 stool samples from 714 mother–infant pairs in the Dutch Lifelines NEXT cohort, spanning 12 weeks of pregnancy to one year after birth.
• The maternal gut was the single largest source of the infant’s early gut bacteria, dwarfing vaginal and breast-milk contributions.
• Mothers of eczema-affected infants had lower gut microbial alpha diversity during pregnancy, an association that survived adjustment for smoking and family allergy history.
• Eczema is common: worldwide point prevalence is 16.0% in children aged 0–5, the peak age group (systematic analysis, Ann Allergy Asthma Immunol 2024).
• The evidence is associative. It does not mean any pregnant person can prevent eczema by taking a probiotic, and standard care still runs through your paediatrician and the skin barrier.

What the 2026 Nature study actually found

Researchers led by the University Medical Center Groningen followed 714 mothers and their infants in Lifelines NEXT, a Dutch birth cohort. They collected 4,526 longitudinal faecal samples from 12 weeks of pregnancy through one year postpartum, plus ultra-deep sequencing of breast milk and vaginal microbiomes, and paired the biology with 474 clinical and exposure variables.

Three findings stand out:

1. The pregnant gut microbiome is remarkably stable. Composition shifted only subtly across pregnancy and postpartum, nudged by diet, infections, and pre-pregnancy smoking. This overturns the older idea of a large third-trimester upheaval.
2. The maternal gut is the main reservoir for infant strains. Bacteria that colonised the infant gut mostly traced back to the mother’s own gut, not to her vaginal or breast-milk microbiomes, which contributed only occasionally. Strain sharing was time-dependent and rose with how abundant a species was in the mother.
3. Lower maternal alpha diversity tracked with infant eczema. Mothers whose infants developed eczema during year one had lower gut microbial alpha diversity in pregnancy. The signal remained after accounting for maternal smoking and family history of allergic disease, both established risk factors.

Alpha diversity counts how many bacterial species share a colon and how evenly they are distributed. More is generally better, and the same measure has been tied repeatedly to gut and metabolic outcomes in adults.

Why the maternal gut shapes the baby’s

At birth a newborn is nearly sterile. Within days their gut fills with bacteria drawn from every surface they touch. The 2026 data settles a long-running debate about which of those surfaces matters most.

Delivery mode still matters, but less than expected

Delivery route and feeding were the strongest shapers of how the infant microbiome developed over the first year. That fits earlier work showing caesarean-born infants get a delayed Bacteroides colonisation. What the Nature paper adds is that even accounting for delivery, the mother’s own gut is the dominant strain donor. Vaginal seeding at birth turns out to be a smaller channel than vaginal-swab clinical trials had assumed.

Breastfeeding shapes what colonises, not what’s on offer

Breast milk carries live bacteria and prebiotic human milk oligosaccharides. The 2026 study found breast milk contributed strains only occasionally, but breastfeeding still strongly patterned which bacteria took hold, likely by selectively feeding them. This lines up with the general principle behind probiotics versus prebiotics: the food matters as much as the bug.

How a mother’s microbes could influence eczema

The paper is careful to describe an association, not a mechanism. Two plausible pathways connect the two.

The first is immune training. The first year is when the neonatal immune system learns to tolerate harmless proteins on skin and in the gut. Diverse early gut colonisers push regulatory T-cell development. A narrower maternal reservoir hands the baby a narrower starter kit, which may skew immune priming toward the Th2 allergic pathway that drives atopic dermatitis.

The second is short-chain fatty acids. Bacteria that ferment fibre make butyrate, acetate, and propionate. These molecules signal to gut and skin immune cells and dampen inflammation. Fewer producers in the mother means fewer producers in the baby’s starter culture.

The NIH’s NIAID has separately documented that people with eczema often carry a distinctive skin microbiome, and that adding a healthy skin commensal (Roseomonas mucosa) can ease symptoms in children. The gut and skin sides of the story are converging on the same word: diversity.

How common is baby eczema, and when does it start?

Eczema, or atopic dermatitis, is the most common chronic skin condition in early childhood. A worldwide systematic analysis covering 2000 to 2021 estimated 16.0% point prevalence in children aged 0–5, the peak group, with 11.1% across all children and adolescents and 6.3% in adults. In 2021 there were an estimated 72.4 million pediatric cases globally, a 6.2% rise since 2000.

Roughly 60% of people with eczema develop it during the first year of life and 90% by age five. In infants under six months the rash usually shows on the scalp and face — forehead, cheeks, chin, around the mouth. After six months it tends to move to the folds of the elbows and knees.

What this means if you’re pregnant or trying to conceive

The temptation is to run to a probiotic aisle. Resist it, at least until better trials arrive. What the evidence supports right now:

1. Eat for microbial diversity. A varied plant-forward diet with plenty of fibre is the single most reproducible way to raise gut alpha diversity in adults. Aim for 25–38 g of fibre per day depending on age and sex — see our fibre and stool consistency guide for a practical approach.
2. Avoid unnecessary antibiotics. Antibiotics collapse diversity, sometimes for months, as covered in antibiotic recovery of the gut microbiome. Take them when a clinician says you need them; skip them for viral infections.
3. Do not smoke. Pre-pregnancy smoking was one of only three exposures that reliably nudged the maternal gut microbiome in the Lifelines NEXT data, and it is an independent eczema risk factor.
4. Breastfeed if you can, without guilt if you cannot. Breastfeeding selectively feeds the strains you did transfer. Formula-fed infants still assemble healthy microbiomes; the difference is a lever, not a verdict.
5. Talk to an obstetrician before adding probiotics. Some prenatal probiotic trials for allergy prevention show a small effect, most show none, and the strains and doses are not standardised. This is not a place to self-prescribe.

What this does not mean

The paper links maternal diversity to eczema; it does not prove that raising your diversity will prevent your baby’s eczema. Family history of atopy remains the largest known risk factor. Filaggrin gene variants that weaken the skin barrier drive a large share of moderate-to-severe cases, and no dietary tweak edits your DNA.

Eczema is also treatable. Standard care works for most babies: daily moisturisers, short lukewarm baths, and topical corticosteroids or non-steroid alternatives for flares. If a rash is spreading, weeping, or waking your infant at night, that is a paediatrician visit, not a microbiome question.

Frequently asked questions

Does a c-section cause eczema?

Not directly. Caesarean delivery is associated with a slightly higher eczema risk in some cohorts, but the 2026 Nature study found the mother’s own gut microbiome mattered more than the delivery route for which strains ended up in the infant. Vaginal seeding after c-section has not been shown to change eczema outcomes.

Should pregnant women take probiotics to prevent baby eczema?

The evidence is mixed and strain-specific. Some perinatal Lactobacillus rhamnosus trials show a modest reduction in eczema; most probiotic strains show no effect. There is no consensus recommendation from major bodies. Ask an obstetrician who knows the specific product before starting anything in pregnancy.

Can breastfeeding prevent baby eczema?

Breastfeeding has small protective associations with eczema in some studies and none in others. The 2026 data shows breastfeeding shapes which of the mother’s strains take hold in the infant, which is one plausible route. Feed the baby the way that works for your family; the microbiome benefit is one small factor among many.

If my baby has green or unusual stool, is that linked to future eczema?

Not established. Infant stool colour reflects transit time, bile, iron intake, and diet more than allergy risk. Our guide on green stool in infants covers when to call the paediatrician.

At what age does baby eczema usually start?

Most cases appear before six months, on the scalp and face. About 60% of people with eczema develop it in the first year of life and 90% by age five, per the worldwide prevalence analysis cited above.

Can I test my gut microbiome to know my baby’s risk?

Consumer stool tests report alpha diversity but their clinical utility for predicting a baby’s eczema is unproven. We covered the general limits of these tests in is gut microbiome testing worth it. Do not make pregnancy decisions on a single at-home report.

The bottom line

The 2026 Nature paper is the strongest evidence yet that the microbes a mother carries in pregnancy influence the microbes her baby will assemble, and that the diversity of that starter kit is measurably linked to eczema in the first year. It shifts the picture from “vaginal seeding fixes everything” to “the mother’s whole gut is the reservoir.” It does not hand parents a preventive protocol. It hands them another reason to protect maternal gut health with the same boring, effective tools that already work: fibre, avoiding unnecessary antibiotics, not smoking, and eating a varied diet.

If you already track your own gut health, keep going through pregnancy — a decent stool log is more useful to your clinician than any single at-home test. PoopCheck turns that log into a photo and two seconds.

Sources

1. Sinha T, et al. Maternal influences on infant gut microbiome and health. Nature, 2026. https://www.nature.com/articles/s41586-026-10922-9
2. National Institute of Allergy and Infectious Diseases (NIAID). Eczema Treatment. https://www.niaid.nih.gov/diseases-conditions/eczema-treatment
3. Tian J, et al. Worldwide prevalence of atopic dermatitis in children between 2000 and 2021: a systematic analysis. Annals of Allergy, Asthma & Immunology, 2024. https://pubmed.ncbi.nlm.nih.gov/39674276/