We spend approximately 90% of our lives indoors — in homes, offices, schools, and hospitals — yet the quality of the air in those spaces receives far less attention than outdoor air pollution. Indoor air quality testing is the discipline that bridges that gap: a rigorous, evidence-based approach to understanding what building occupants are actually breathing, identifying the biological and chemical sources of risk, and informing the measures needed to protect health.
In this post, Natasha Gordon of Airmid Healthgroup explores the science behind poor indoor air quality, the health conditions it can trigger, the microbial and chemical hazards most commonly encountered in the built environment, and what modern international standards now require of employers and building managers.
Sick Building Syndrome: Still Relevant, Still Underestimated
The term “Sick Building Syndrome” (SBS) was first used to describe a building in which complaints of ill health are more common than might reasonably be expected — a definition that has not lost its relevance in the four decades since it was coined (Finnegan et al., 1984). The medical conditions associated with poor indoor air quality encompass eye, ear, nose and throat irritation; wheeze and chest tightness; headaches and nosebleeds; skin sensitisation; cognitive fatigue and general lethargy; and the worsening of pre-existing asthmatic conditions.
In the years since the term was introduced, the evidence base for causative factors has expanded substantially. Professional indoor air quality testing now routinely measures biological contaminants — including fungi, bacteria and allergens — alongside chemical pollutants such as volatile organic compounds (VOCs), formaldehyde, and carbon dioxide, each of which has been associated with the symptom cluster that defines SBS. The fundamental challenge remains: the indoor environment is multifactorial, and poor IAQ rarely has a single cause.
Fungal and Microbial Contamination in the Built Environment
Fungal and bacterial microorganisms are a ubiquitous element of the flora that any building occupant is exposed to on a daily basis. Under the right conditions — elevated humidity, inadequate ventilation, and the presence of suitable substrate materials — these organisms can proliferate to concentrations that represent a genuine health risk.
Many materials used in modern building construction and interior fit-out contain cellulose, the primary structural polysaccharide of plant cell walls. As moulds commonly function as saprophytes — organisms that acquire nutrients from decaying organic matter — cellulose represents an excellent growth substrate. Evidence demonstrates that its presence in building materials such as ceiling tiles, plasterboard, joinery, and insulation boards favours mould colonisation and proliferation (Karunasena et al., 2001). Certain mould genera, including Aspergillus, Penicillium, Stachybotrys, Cladosporium, Mucor and Alternaria, as well as species from the phylum Basidiomycota, have been heavily implicated in fungal infection and sensitisation reactions acquired in the indoor environment.
The ability of these fungi to colonise diverse building materials while tolerating significant variation in temperature, moisture and pH presents a particular challenge for individuals with asthmatic fungal sensitisation, who are at elevated risk of developing allergic and asthmatic reactions that can substantially reduce quality of life. For immunosuppressed individuals or those with pre-existing pulmonary conditions such as emphysema, tuberculosis or cystic fibrosis, exposure to elevated airborne fungal counts carries a significantly heightened risk of invasive infection, with mortality rates from such infections remaining notably high. The economic cost — through increased healthcare burden, lost productivity and structural damage to building fabric — makes proactive indoor air quality testing and remediation a sound investment rather than an optional extra.
The seasonal dimension of microbial IAQ risk is also significant. Natural ventilation in office and commercial buildings typically decreases during autumn and winter as occupants conserve heat. The cumulative effect of increased indoor humidity from inadequate ventilation, combined with a seasonal rise in ambient airborne mould levels, means that the incidence of IAQ-related health issues tends to peak during these months.
HVAC Systems and the Importance of Indoor Air Quality Testing
Modern commercial buildings rely heavily on HVAC (heating, ventilation and air conditioning) systems for ventilation and thermal regulation. When correctly specified and maintained, HVAC systems are an effective tool for managing indoor air quality. When neglected, they can become a primary source of IAQ problems — and given the recirculation of air inherent in their operation, a contaminated system can exert a sustained adverse influence on air quality throughout an entire building.
The risks associated with Legionella contamination in HVAC units and cooling towers are widely understood and appropriately regulated. Less well-appreciated is the fact that inadequate maintenance of ductwork and air handling units has also been directly linked to elevated airborne counts of other pathogenic bacteria and fungal microorganisms. At Airmid Healthgroup, we have observed a consistent correlation between ductwork contamination and elevated airborne microbial counts in occupied spaces — a finding that underscores the importance of including microbiological duct sampling as part of any comprehensive indoor air quality testing programme.
HVAC operation also affects key physical parameters. Low relative humidity (below 40%) — common in winter when cold incoming air is heated and recirculated — dries mucous membranes, compromising a primary natural defence against airborne pathogens. Elevated carbon dioxide concentrations resulting from insufficient fresh air supply have been shown to reduce occupant cognitive performance and concentration over time. Both are readily quantified by indoor air quality testing and are actionable through ventilation adjustment or supplementary air cleaning.
International Standards for Indoor Air Quality
The regulatory and standards framework for indoor air quality has strengthened considerably in recent years, driven by post-pandemic awareness of airborne transmission risk and by the growing body of evidence linking chronic exposure to poor indoor air with serious long-term health outcomes.
The WHO Global Air Quality Guidelines (2021) represent the most rigorous internationally agreed thresholds to date, setting updated guidance for particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide — a significant tightening of the previous 2005 recommendations. These guidelines increasingly inform national legislation and building certification frameworks worldwide.
ASHRAE Standard 62.1 (Ventilation and Acceptable Indoor Air Quality) specifies minimum ventilation rates and other measures intended to deliver acceptable indoor air quality in commercial and institutional buildings. It underpins building codes across North America and is referenced in international building performance standards.
ASHRAE Standard 241 (Control of Infectious Aerosols), published in 2023, goes further — establishing specific requirements to reduce the risk of airborne transmission of infectious agents in occupied spaces. Its provisions for equivalent clean air delivery, filtration performance and air cleaning technology are directly assessable through indoor air quality testing, and are increasingly being cited by building owners and facility managers as a benchmark for healthy building performance.
Within the European Union, the revision of the Energy Performance of Buildings Directive (EPBD) increasingly integrates indoor air quality provisions alongside energy efficiency targets, reflecting policy recognition that the two objectives must be pursued in parallel rather than in opposition. Employers across the EU and globally also operate under a general duty of care to employees that encompasses providing adequate ventilation and air quality in enclosed workplaces — a duty that a structured indoor air quality testing and monitoring programme is specifically designed to document and discharge.
The Business Case for Regular Indoor Air Quality Testing
Beyond regulatory obligation, the operational and financial case for proactive indoor air quality testing is well-established. Research consistently demonstrates that improved ventilation and reduced airborne contaminant loads are associated with measurable improvements in cognitive task performance, reduced absenteeism and higher self-reported wellbeing among building occupants (Allen and Macomber, 2020). Poor indoor air quality imposes direct costs — through sick days, reduced productivity and healthcare — that dwarf the investment required for regular monitoring and remediation.
Proactive indoor air quality testing also provides documented evidence of compliance, which is increasingly important in an environment of heightened occupant awareness, growing litigation risk, and more frequent regulatory inspection. For facilities teams, the data generated by regular air quality audits provides the foundation for evidence-based maintenance decisions, enabling targeted intervention before microbial colonisation becomes visible or symptomatic — and before it triggers the costly reactive remediation that follows neglect.
Indoor Air Quality Testing with Airmid Healthgroup
Airmid Healthgroup combines expertise from aerobiologists, microbiologists and medical professionals to deliver comprehensive indoor air quality testing services for commercial premises, industrial environments and residential buildings. Our capability spans airborne microbiological sampling — including bacteria, fungi and allergens — through to chemical and physical parameter measurement covering VOCs, CO₂, particulate matter, temperature and relative humidity.
Our ISO/IEC 17025-accredited laboratory provides the scientific rigour that underpins actionable, defensible results. Whether you are responding to occupant health complaints, conducting a due diligence assessment, seeking to demonstrate compliance with ASHRAE 241 or EU building standards, or simply committed to providing a genuinely healthy working environment, Airmid Healthgroup has the expertise and accreditation to support you.
Contact Airmid Healthgroup to discuss your indoor air quality testing requirements.
References
Finnegan, M.J., Pickering, C.A.C. and Burge, P.S. (1984). The sick building syndrome: prevalence studies. British Medical Journal, 289: 1573–1575.
Karunasena, E., Markham, N., Brasel, T., Cooley, J.D. and Straus, D.C. (2001). Evaluation of fungal growth on cellulose-containing and inorganic ceiling tile. Mycopathologia, 150: 91–95.
World Health Organization (2021). WHO Global Air Quality Guidelines: Particulate Matter (PM2.5 and PM10), Ozone, Nitrogen Dioxide, Sulfur Dioxide and Carbon Monoxide. Geneva: WHO Press.
ASHRAE (2023). ASHRAE Standard 241: Control of Infectious Aerosols. Atlanta: ASHRAE.
Allen, J.G. and Macomber, J.D. (2020). Healthy Buildings: How Indoor Spaces Drive Performance and Productivity. Cambridge, MA: Harvard University Press.
About the Author
Natasha Gordon writes on indoor air quality and occupational health for Airmid Healthgroup, applying a background in environmental science to the practical challenges of building-related illness, microbial contamination and IAQ audit methodology.
About Airmid Healthgroup
Airmid Healthgroup is a GLP and ISO/IEC 17025-accredited contract research laboratory specialising in aerobiology, infectious aerosol testing, indoor air quality testing, and antimicrobial efficacy testing. With clients across medtech, consumer products, HVAC, and the built environment, Airmid Healthgroup helps innovators generate the scientific evidence needed to validate performance claims, meet regulatory requirements and protect end-user health.
