News · Longevity & Aging
Children with the most early infections had about 60% more eczema, not less
The hygiene hypothesis says early germs train the immune system and protect against allergic disease. Two birth cohorts with daily symptom diaries found the opposite direction for eczema.
- Toddlers with the most infections had more eczema later, not less.
- That runs against the idea that early germs protect against allergic disease.
- The pattern held after accounting for antibiotics and a known skin-barrier gene.
- It repeated in a second, separate birth cohort in the US.
- Infections were logged in daily diaries rather than remembered years later.
For forty years the standard story about allergic disease has run in one direction. Children raised too clean, with too few infections and too little dirt, grow up with immune systems that have never had proper practice and turn on harmless things instead.
It is a good story with real evidence behind it, particularly for farm exposure and asthma. It also gets applied loosely, to every allergic condition at once, as though eczema and hay fever and asthma were one disease.
Researchers writing in the journal JAMA Dermatology tested it for eczema specifically, and found the arrow pointing the other way. Whether early-life infections are associated with the condition remains unclear, they note, and among 663 children in COPSAC2010 the children who had more infections had more eczema.
What was counted, and how
The measurement is the reason to take this seriously. Most studies of childhood illness ask parents to recall it, years later, after a diagnosis has already colored the memory.
This cohort used daily diary-registered infection episodes covering colds, ear infections, tonsillitis, pneumonia, gastroenteritis and fever, recorded as they happened up to age 3. Eczema was then tracked to age 10 using diagnostic criteria and a severity score rather than a parent’s impression.
Children in the top third for number of infection episodes had around 60% more eczema across those ten years than children in the bottom third. Counting infection days rather than episodes gave a slightly larger figure.
The two things that had to be ruled out
Any finding like this immediately raises two objections, and the analysis addresses both.
The first is antibiotics. Children who get more infections get more antibiotics, and antibiotic exposure has been separately linked to eczema through effects on the microbiome. The analyses adjusted for systemic antibiotic treatments, so the association is not simply an antibiotic effect wearing an infection costume.
The second is genetics. Eczema is a term for several different types of skin swelling, and a substantial share of it traces to variants in the filaggrin gene, which builds the skin barrier. A weak barrier could plausibly produce both more skin infections and more eczema. The analysis adjusted for filaggrin status too.
Replication, which is the part that counts
A single cohort of 663 children producing an effect this size, with a wide margin of uncertainty around it, is a hypothesis rather than a finding.
What lifts it is that the authors went looking for the same pattern in an entirely separate birth cohort, the US Vitamin D Antenatal Asthma Reduction Trial, with different families, a different country and a different way of recording both the infections and the diagnosis.
Seeking replication in a second cohort before publishing is not standard practice in this field. It should be.
The objection that survives
Reverse causation is not disposed of by either adjustment, and the authors do not claim it is.
Eczema frequently begins in the first months of life, before most of the infections in this study were recorded. Skin that is already broken is easier for organisms to cross, and children with early skin disease may simply be children who then get ill more often.
If that is what is happening, the infections are a consequence of early eczema rather than a cause of later eczema, and the entire direction of the finding reverses. Nothing in an observational birth cohort can separate those two orderings cleanly.
Why it matters even unresolved
The hygiene hypothesis has entered general circulation as advice. Let children get dirty, do not over-sterilize, a few colds are good for them.
Some of that is well founded. What this study shows is that it does not transfer automatically to every allergic condition, and that for eczema the association in two independent cohorts runs the wrong way for the popular version of the story.
That is a correction to a piece of received wisdom rather than an instruction to anyone. Nobody should be trying to prevent their toddler’s colds on the strength of it, and nobody should be arranging extra ones either.
People also ask
What did the study find?
Children in the upper versus lower tertile of infection episodes had higher yearly eczema prevalence from ages 0 to 10 (adjusted odds ratio 1.61; 95% CI 1.05-2.47; P = .03), and for infection days 1.69 (95% CI 1.11-2.58; P = .01). Analyses adjusted for filaggrin variant status and systemic antibiotic treatment.
What is the hygiene hypothesis?
The long-standing idea that early exposure to microbes trains a developing immune system, and that too little exposure leaves it prone to allergic conditions such as eczema, asthma and hay fever. This result points the other way for eczema specifically.
Why does the diary method matter?
Because most studies ask parents years afterwards how often a child was ill, and memory is shaped by what happened since. Here symptoms were recorded daily as they occurred, which removes a large source of error.
Could eczema be causing the infections rather than the reverse?
That is the central alternative. Broken skin is easier for bacteria to cross, and eczema often starts in the first months of life, so early skin disease could be driving both the infections and the later diagnosis.
What is the filaggrin gene?
A gene that helps build the skin barrier. Certain variants weaken it and strongly raise eczema risk. The analysis accounted for it, which matters because it could otherwise explain both more skin infections and more eczema.
Was it confirmed anywhere else?
The authors sought replication in a second birth cohort, the US Vitamin D Antenatal Asthma Reduction Trial, which recorded colds, fevers and respiratory infections to age 3 with parent-reported eczema diagnosis to age 6.
Should parents do anything differently?
No. Nothing here says to avoid normal childhood illness, which is neither possible nor desirable, and it does not identify anything a parent should change. This is general information rather than medical advice.