June 15, 2026

Understanding CIRS: Why Genetic Susceptibility Demands a New
Standard for Indoor Environmental Investigation
Why the 25% / 75% split is the most important graphic in our profession — and what it means for how IEPs are trained, certified, and held accountable.
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The Illness, Defined
Chronic Inflammatory Response Syndrome (CIRS) is a multi-system, multi-symptom illness triggered by exposure to biotoxins — most commonly the inflammagens generated inside water-damaged buildings (CIRS-WDB). It is not allergy. It is not psychosomatic. It is a measurable disruption of innate and adaptive immune signaling, supported by validated biomarkers, neuroimaging findings, and a published
treatment protocol.
 
At HBIA, we treat CIRS as the case study that defines our profession. If we can investigate a building well enough to support a CIRS recovery, we can investigate any building.
 
Two Pathways, One Exposure
The infographic above tells the story in a single image. The same biotoxin exposure produces two radically different outcomes depending on a single variable: the patient's HLA-DR/DQ haplotype.
 
The Susceptible 25%
In genetically susceptible individuals, the adaptive immune system fails to register the biotoxin. The innate alarm keeps firing. The toxin moves cell to cell. What follows is a six-step cascade:
 
          Exposure to biotoxin
          Innate immune system sounds the alarm
          Adaptive immune system fails to respond — toxin persists — innate signaling escalates
          Biotoxins migrate cell-to-cell, damaging the immune system itself
          System-wide inflammation takes hold
          Multi-system symptoms emerge — including documented gray matter changes on volumetric MRI
 
The Non-Susceptible 75%
In the majority of the population, the adaptive immune system hears the innate signal, binds the biotoxin, and clears it through the biliary route. The exposure is metabolized and the patient walks

away. The asterisk, however, is critical: continuous exposure to a water-damaged building can overwhelm clearance in any genotype. No one is immune to a sick building indefinitely.
 
What This Means for the IEP
For decades, the indoor environmental industry has been organized around a single question: "Is there visible mold?" That question is inadequate for CIRS-affected patients. By the time a susceptible patient is symptomatic, the relevant exposure is rarely visible — it is microbial fragments, mycotoxins, endotoxins, actinobacteria, and inflammagens carried on settled dust.
 
A practitioner-grade investigation for a CIRS patient requires:
 
     Targeted dust-based microbial assays (HERTSMI-2 and/or ERMI) interpreted against clinical thresholds, not generic comparison.
          Moisture and building science forensics that identify the source pathway, not just the visible
damage.
          Reporting structured for clinical use — formatted so the treating physician can act on it directly.
     A consistent national protocol so that a CIRS patient in Maryland receives the same standard of investigation as a CIRS patient in California.
 
Why  HBIA Exists
The Healthy Building Institute of America (HBIA) was built to close the gap between functional medicine and indoor environmental assessment. The CIRS pathway in the infographic is the reason we exist as a standards body. When 1 in 4 patients cannot clear biotoxins on their own, the building investigation is not a service — it is a clinical intervention.
 
Our current Field Trial Study is the operational expression of that mission: a multi-state effort bridging functional medicine clinicians with HBIA-trained IEPs, capturing the data needed to demonstrate that medically-informed environmental investigation changes patient outcomes.
 
The Bottom  Line for Practitioners
If you treat CIRS, MCAS, Lyme,  or any chronic complex illness, the building is part of the patient. The 25%
/ 75% split is not a curiosity — it is the reason an unremarkable environmental report can sit in a chart for years while a patient gets worse. The remedy is not more testing. It is the right testing, interpreted by professionals trained to the same national standard.
 
That is what HBIA is building. Practitioners, IEPs, and remediation professionals interested in the certification pathway or the Field Trial Study can reach us at www.hbiatoday.com.
 
 
 
 
— HBIA | The Healthy Building Institute of America