What You Should Know About Mold Risks in Air-Conditioners

Air-conditioners provide vital relief during scorching weather, yet they may also introduce health hazards, particularly from mold contamination.

This concern was recently underscored when the manufacturer Midea recalled nearly 1.7 million units due to a design defect that promoted mold development.

Although this specific flaw increased mold risks, any air-conditioning system can develop mold regardless of its design quality. Fortunately, there are practical steps to minimize this danger.

The key factor behind mold growth is moisture accumulation.

Whether using a window unit or central air system, air-conditioners function by cycling refrigerant between gas and liquid states. During evaporation, the refrigerant absorbs heat through the evaporator coil. A fan then circulates the cooled air indoors while expelling warm air outside, allowing the refrigerant to condense and repeat the cooling cycle.

As warm air cools, condensation forms—much like water droplets appearing on the exterior of a chilled glass. Inside the air-conditioner, a drain pan collects this moisture. Properly designed systems channel this water outside, preventing stagnation. However, drainage failures or design imperfections can leave moisture trapped inside.

This retained moisture creates an environment conducive to mold growth, as explained by an expert in indoor air pollution and epidemiology, who noted that water can accumulate without proper drainage, becoming contaminated, and then air passing over it carries spores into the living space.

Although air-conditioners are widespread and susceptible to mold, scientific research specifically addressing their health impacts remains limited.

One notable study from 2003 found that exposing cooling coils and drain pans in office air-conditioning systems to ultraviolet light, which kills bacteria and fungi, corresponded with fewer reported respiratory symptoms among workers.

Generally, conclusions are drawn from broader research on indoor dampness and mold exposure rather than air-conditioners alone.

A 2011 review linked dampness and mold exposure to increased asthma flare-ups, coughing, wheezing, and upper respiratory issues, though it stopped short of confirming mold as the definitive cause. A subsequent 2015 review found sufficient evidence to associate dampness and mold with worsening asthma symptoms in children.

Researchers observe that symptoms tend to be more common in buildings where mold is visible or detectable by smell, yet direct correlations between specific fungal concentrations and health effects have not been conclusively established. It remains possible that current measurements overlook relevant mold types or that other factors contribute.

As one expert summarized, it seems probable that some microbial exposures related to dampness are responsible for health problems, but definitive proof is still lacking.

Routine upkeep of air-conditioners—such as cleaning or replacing filters monthly—can help deter mold formation. Many window units feature indicators signaling when maintenance is needed.

Maintaining controlled indoor humidity levels, possibly with the aid of a dehumidifier, is beneficial regardless of the type of air-conditioning system. Keeping the home clean reduces dust accumulation, which serves as nourishment for mold spores. Utilizing an air purifier can further remove dust and mold particles from the air.

These preventive measures, however, do not guarantee elimination of mold risk. Periodic inspections of the air-conditioner are advisable, especially after prolonged inactivity such as during winter months.

Visible mold may be found near vents, and using a flashlight can help detect hidden growth. For those comfortable with DIY tasks, disassembling window units as per the manufacturer’s guidelines allows for thorough cleaning of coils and drain pans.

Comprehensive cleaning instructions for both window and central air-conditioning systems are available for those seeking detailed guidance.