On April 23, 2026, the GO AQS Mould/Mold Working Group convened to synthesize findings from expert surveys, global standards, and current scientific literature to establish a unified approach to indoor mould management. The call brought together experts from the United States, Europe, Asia, and Australia, highlighting a significant consensus on moving away from rigid, absolute numerical limits toward a more dynamic and proactive trigger level model. One of the initial points of discussion was the intentional use of both “mould” and “mold” in all official communications to ensure global searchability and regional inclusivity across different standard-setting bodies.

A central conclusion of the working group is that absolute numerical limits are unreliable because background mould levels vary drastically by geography and season, making a universal “safe” number impossible to define. Instead, the group favors comparative logic, where indoor environments are evaluated against their immediate outdoor surroundings to identify anomalies. Furthermore, the group established that there is no linear dose-response relationship for mould exposure; because individual sensitivity varies as widely as a peanut allergy, a count that is safe for one person could represent a health crisis for another. This variability led to a unanimous agreement that infants, the elderly, and the immunocompromised require distinct and more stringent protective thresholds.

The discussion emphasized that moisture management is the only definitive way to control mould, asserting that sampling should always be secondary to identifying and fixing the water source. This includes not only fixing structural leaks but also addressing poor building performance, such as inadequate ventilation and air change rates that allow moisture to collect. Experts highlighted that relative humidity above 60% should serve as a primary proactive indicator of risk, though more advanced metrics like moisture mass and dew point were recommended for a more accurate assessment of condensation potential. The use of IoT sensors was praised for its ability to make “the invisible visual,” allowing building managers and occupants to monitor performance and maintain a cycle of continuous improvement.

The working group also identified mould odor, or Microbial Volatile Organic Compounds (MVOCs), as the strongest predictor of respiratory illness, often indicating a hidden fungal ecology even when mould is not visible. While traditional air sampling can underestimate total exposure by missing non-culturable or dead spores, monitoring MVOCs provides a more neutral and clinically relevant data point. The group also noted the impact of building materials, observing that traditional stone resists growth even in high humidity, whereas modern porous materials like drywall are far more susceptible. Ultimately, managing these risks is a shared responsibility; landlords must ensure structural integrity and ventilation, while occupants must be educated on reducing internal moisture loads.

The call concluded with the determination that these insights will form the basis of a holistic public health strategy focused on rapid identification and remediation.

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Next Step

As the next step in this process, working group members will be asked to review and provide feedback on the final recommendations to ensure they are accurately represented before their formal inclusion in the global open standard.