Back-to-back infections read like a rough season or a weak immune system. A 27-year Finnish cohort adds another suspect: a damp home — and the effect grew the longer the damp stayed.
Mold usually gets filed under allergy and asthma. A long-running Finnish study points at something more ordinary: how often you catch a cold or a chest infection in the first place. Researchers followed the same people from early childhood to age 27 and found that those living with dampness or mold reported more upper-airway infections and, more strikingly, more infections in the chest — and the risk climbed with every added stretch of exposure.
What the study measured
Joona Maaranen and colleagues at the University of Oulu followed the Espoo Cohort: 2,568 people in Finland, tracked from early childhood to age 27 and published in the American Journal of Epidemiology in 2025. At three points across those years, people reported four signs of a damp home — water damage, moisture on surfaces, visible mold, and mold odor. The team then counted upper-respiratory infections (colds, sinus infections, tonsillitis, ear infections) and lower-respiratory infections (acute bronchitis and pneumonia), and checked the questionnaire counts against national hospital and care registers.
+15% upper-airway infections · +47% chest infections. Higher incidence among people in a damp or moldy home versus a dry one, pooled across 27 years (Maaranen et al., 2025).
What they found
Pooling all three follow-ups, a home with any dampness or mold came with about 15% more upper-respiratory infections (adjusted incidence rate ratio 1.15, 95% CI 1.10 to 1.21) and 47% more lower-respiratory, chest, infections (aIRR 1.47, 95% CI 1.21 to 1.79). Both held after adjusting for sex, family socioeconomic status, breastfeeding, and tobacco smoke before and after birth. The signs did not all carry the same weight: for chest infections, water damage was tied to a 2.16-fold rate (95% CI 1.38 to 3.36) and mold odor to a 2.43-fold rate (95% CI 1.32 to 4.47) — both more than a doubling. Visible mold on its own did not reach significance for chest infections, so the clearest signal sat with water damage, dampness, and smell.
The part that keeps climbing
The most useful finding is about time. In the detailed childhood analysis, each added period of exposure raised the rate again: about 10% more upper-respiratory infections (aIRR 1.10, 95% CI 1.06 to 1.15) and 31% more chest infections (aIRR 1.31, 95% CI 1.13 to 1.53) per extra exposure window. By young adulthood, people with a damp history still had 15% more upper-airway infections and more than double the chest infections (aIRR 2.15, 95% CI 1.37 to 3.37). And the register data — actual medical visits rather than memory — tied childhood dampness or mold to a 70% higher rate of upper-airway infections needing a doctor by age 27. A damp problem left in place does not hold steady; the count rises the longer it sits.
Why dampness would raise infections
The authors describe damp, warm building materials breaking down and releasing spores, particles, and microbial byproducts into the air. Repeated exposure irritates and inflames the airway lining, which plausibly leaves it slower to clear the everyday viruses and bacteria everyone meets. Damp buildings also grow more bacteria, not only mold, and some of that may matter as much as the mold itself. That mechanism is inferred from the biology, not proven inside a questionnaire study.
What this means for your home
The good news is that this exposure is fixable, because it is really about water. Keep indoor humidity in a reasonable range (roughly 30 to 50 percent). Run the bathroom and kitchen exhaust fans and vent them outside, clear condensation off cold windows, and repair leaks before the drywall stays wet for weeks. Because the risk stacks with duration, speed matters: a damp problem handled in weeks beats one left for seasons. Follow your nose, too — a musty smell was one of the strongest signals here, even where nothing was visible. A 2015 Cochrane review of repairing damp, moldy buildings found that remediation reduced respiratory symptoms and infections, and you do not need to name a fungus to benefit from drying the place out.
A note on certainty: exposure and most infections were self-reported, so some misclassification is built in, and a worried parent may notice damp walls more, which would inflate the link. The study is observational: it shows association, not cause. Visible mold alone was not significant for chest infections. What survives all of that: across a large cohort, three separate follow-ups, and a hospital register, the direction never flipped — more damp, more infection — in a clear dose-response with duration.
Can’t see it? You can still measure it.
illumenair maps moisture and mold room by room in Portland and Vancouver homes, then gives you a plain-language report and a prioritized action plan, so you can act on what you’re breathing instead of guessing. We test the air; we don’t sell remediation.
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Sources: Maaranen J, Hugg TT, Paciência I, Jaakkola MS, Jaakkola JJK, Rantala AK. “Home dampness and molds and occurrence of respiratory tract infections in the first 27 years of life: the Espoo Cohort Study.” American Journal of Epidemiology 2025;194(12):3492–3500. · Sauni R, Verbeek JH, Uitti J, et al. “Remediating buildings damaged by dampness and mould for preventing or reducing respiratory tract symptoms, infections and asthma.” Cochrane Database of Systematic Reviews 2015.