Maintaining indoor air quality (IAQ) is a critical challenge in healthcare, pharmaceutical, and commercial facilities—especially where the risk of airborne microbial contamination is high. While air filtration plays a vital role in removing pathogens from the airstream, it’s only part of the solution. Controlling indoor humidity levels is equally essential, directly influencing how microbes grow, spread, and survive within HVAC systems and occupied spaces.

In this article, we explore how humidity control complements air filtration in reducing microbial contamination, drawing on real-world studies to support its impact.

Why Humidity Matters in Microbial Control

Humidity plays a dual role in pathogen dynamics. When indoor relative humidity (RH) rises above 60%, it creates ideal conditions for mould, bacteria, and fungi to grow—especially on damp surfaces inside HVAC systems. On the other hand, very low humidity (below 30%) can dry out mucous membranes in occupants, weakening the body's natural defences and increasing susceptibility to infections.

Research has shown that maintaining RH between 40% and 60% significantly reduces the survival rate of many airborne pathogens. This "sweet spot" not only limits microbial viability but also contributes to occupant comfort and respiratory health.

How HVAC Systems Become Breeding Grounds

HVAC systems manage large volumes of air while simultaneously handling moisture, especially in buildings with high occupancy or varying external climates. Moisture commonly accumulates on evaporator coils, in drip pans, and inside ductwork—particularly if airflow is obstructed or maintenance is inconsistent.

When left unchecked, these moist surfaces provide the perfect environment for microbial biofilms to form. These colonies can release spores and bacteria back into the air, bypassing even high-quality filters if growth occurs downstream in the system.

Real-World Evidence - Humidity Control and Microbial Reduction

A compelling study conducted at Kamyab Hospital in Iran investigated the relationship between indoor environmental conditions and airborne microbial levels. Researchers found a strong inverse correlation between RH and microbial counts—the higher the humidity (within optimal ranges), the lower the concentration of airborne bacteria and fungi. Similar trends were observed with ventilation rates (ACH), highlighting the importance of combining air changes with proper humidity management.

Key Result: Both relative humidity and air change rates had a statistically significant (P = 0.001) impact on reducing microbial contamination in hospital airspaces.

Additionally, a meta-analysis of 21 hospital environments showed that air-conditioned areas with active humidity and filtration controls consistently demonstrated lower microbial counts compared to naturally ventilated spaces. These findings reinforce the practical value of humidity regulation as a tool for infection control, particularly in high-risk settings like surgical suites, ICUs, and cleanrooms.

Effective Strategies for Humidity Control

Implementing humidity control requires both system design and ongoing maintenance. Strategies include:

• Dehumidifiers: Desiccant or refrigerant-based units can be integrated into HVAC systems to maintain RH below 60% in humid environments.
• Humidifiers: In dry climates, properly maintained steam or evaporative humidifiers prevent RH from dropping too low, especially in winter.
• Sensor Integration: Smart controls and RH sensors should be installed at multiple points, not just in return air ducts. Integration with the Building Management System (BMS) allows for real-time adjustments.
• Drainage Management: Ensuring that condensate drains are functioning correctly is key to preventing stagnant moisture and microbial growth in trays or pans.

Design Considerations for Microbial Risk Reduction

Humidity control should be factored into the very architecture of an HVAC system, not treated as an afterthought. Key design principles include:

• Zoned control to maintain different RH levels in different parts of a building.
• Access points for easy inspection and cleaning of moisture-prone components.
• Airflow optimisation to prevent stagnant zones where condensation can occur.

Partnering with manufacturers like Air Options—who specialise in bespoke AHU solutions for clean air environments—ensures that these considerations are built into your system from the ground up. With extensive experience across healthcare, food processing, and industrial sectors, Air Options delivers equipment that supports both humidity stability and infection control standards.

Air Options - A Dual Approach to Cleaner Air

Filtration systems are essential for removing microbes from the air, but controlling humidity addresses the root causes of microbial growth—making both strategies necessary for long-term effectiveness. Real-world hospital studies have validated that environments with optimal RH and good air circulation show dramatically reduced airborne microbial loads.

At Air Options, we understand that microbial risk is not solved with a single intervention—it requires a systems-level approach. Our advanced air handling units (AHUs) are designed to support precise humidity regulation, high-efficiency filtration, and custom airflow control—making them ideal for medical, pharmaceutical, and commercial environments where air hygiene is paramount.

If your facility requires a tailored HVAC solution that goes beyond temperature control, we’re here to help design and deliver a system that prioritises long-term health, safety, and compliance.