One Take #24: Association vs. Causation - Why Proving Mold Makes You Sick Is So Hard
Why is it so difficult to prove that mold makes people sick when millions of people clearly suffer in water-damaged buildings?
The association is undeniable. The causation? That's where things get complicated. This episode unpacks a fundamental challenge that has plagued the mold and health field for decades – the seemingly simple but scientifically complex distinction between association and causation. We know with certainty that people in damp, moldy buildings experience more respiratory symptoms, asthma exacerbations, and various health complaints. The 2004 Institute of Medicine report established this definitively, finding "sufficient evidence of an association" between visible mold and respiratory symptoms. But proving that mold directly causes these problems? That's an entirely different scientific mountain to climb. The core challenge lies in what scientists call the Bradford Hill criteria – the gold standard for establishing causation in epidemiology. To prove mold causes illness, we'd need to demonstrate a clear dose-response relationship (more mold equals more illness), temporal relationships (exposure before symptoms), biological plausibility, and ideally, experimental evidence. But here's the rub: mold exposure in real buildings is never just mold exposure. It's a complex soup of fungal spores, bacterial endotoxins, volatile organic compounds, allergens, and chemical emissions from degrading materials. How do you isolate the effect of one component in this biological cocktail?
The Exposure Assessment Black Hole Perhaps the most maddening aspect is our inability to accurately measure what people are actually exposed to. Unlike a drug trial where you know exactly what dose someone received, mold exposure is invisible, variable, and cumulative. A single air sample tells you almost nothing about someone's exposure over weeks or months. Spore counts fluctuate wildly based on humidity, disturbance, and time of day. Some people might react to dead spores or fragments that don't even show up in standard tests. Others might be sensitive to mycotoxins at levels far below what we can reliably detect. This measurement problem creates a vicious cycle. Without good exposure data, we can't establish dose-response relationships. Without dose-response relationships, we can't prove causation. Without proven causation, there's less funding for better measurement tools. And round and round we go. The Human Variability Factor Then there's the inconvenient fact that people react differently to the same environment. Genetics, immune status, age, pre-existing conditions – all these factors influence whether someone develops symptoms in a moldy building. This heterogeneity makes it nearly impossible to predict who will get sick and how sick they'll get, further muddying the causation waters. The episode explores how this scientific uncertainty has real-world consequences. Insurance companies exploit the causation gap to deny claims. Building owners hide behind the lack of "proof" to avoid remediation. Meanwhile, people suffering in water-damaged buildings are told their symptoms might be "all in their head" because science can't definitively prove the mold is making them sick. The Path Forward Despite these challenges, the scientific consensus is clear on one point: water-damaged buildings are unhealthy environments that should be remediated, regardless of whether we can prove specific causal pathways. The precautionary principle applies – we know enough about the associations to act, even if we can't draw straight lines from exposure to illness. This One Take reveals why the mold and health field remains so contentious and why simple questions like "is mold making me sick?" don't have simple answers. It's a sobering reminder that in environmental health, the gap between what we observe and what we can scientifically prove often feels insurmountable – not because the connections aren't real, but because reality is far more complex than our measurement tools and study designs can capture.
Damp Indoor Spaces and Health (2004)
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Ireland