Air conditioning (AC) systems function by regulating indoor temperature and humidity, providing necessary relief from heat and improving comfort, which helps prevent heat-related illnesses like heat stroke. While AC is fundamentally safe and beneficial, certain health issues may arise when systems are improperly used or poorly maintained. Understanding the mechanisms behind these potential effects is the first step toward mitigating any risks associated with indoor cooling.
Respiratory System Irritation
The human respiratory system is highly sensitive to the temperature and moisture content of the air it takes in. Exposure to cold, circulating AC air can trigger an immediate physical response in the nasal passages and throat. Inhaling significantly cooler air causes the small blood vessels in the upper respiratory tract to narrow, a process called vasoconstriction, as the body attempts to conserve heat.
This rapid temperature change, often experienced when moving from a hot outdoor environment into an air-conditioned space, can be jarring. Cold air also causes mucus membranes to dry out. The delicate fluid layer lining the airways, which traps pathogens, becomes less effective when its moisture evaporates quickly. This compromised defense mechanism, combined with dry air irritation, can make the respiratory tract more susceptible to infections or exacerbate existing conditions like asthma.
Maintaining Optimal Hydration and Skin Health
AC units remove moisture through condensation and evaporation, lowering indoor relative humidity. Maintaining an indoor humidity level between 40% and 60% is optimal for comfort and health.
When humidity drops too low, moisture evaporates quickly from the skin, leading to dryness, flakiness, and irritation, especially for individuals with conditions like eczema. Low humidity also accelerates the evaporation of the thin tear film covering the eyes. This can cause eye irritation, a gritty sensation, and temporary blurred vision, particularly affecting contact lens wearers. Increased moisture loss through the skin and breath in a dry environment can also contribute to mild dehydration if fluid intake is not maintained.
The Role of System Contaminants
Health concerns arise from the maintenance state of the AC system, which can harbor and circulate biological and particulate contaminants. AC filters and ducts accumulate common household allergens, such as dust, pet dander, and pollen, which the system recirculates. For individuals with allergies, asthma, or respiratory sensitivities, this dispersal can trigger symptoms like sneezing, congestion, and coughing.
Moisture created by the cooling process collects in drain pans and coils, creating an environment for mold and mildew growth if not properly cleaned. These fungi release spores into the airflow, posing a risk of allergic reactions and respiratory problems.
Legionella Risk
Large-scale cooling systems, such as cooling towers used in commercial buildings, rely on water to cool the refrigerant. Stagnant water in these systems, especially when maintained between 25°C and 45°C, can become a breeding ground for the bacterium Legionella pneumophila. Inhalation of fine mist containing this bacterium causes Legionnaires’ disease, a severe form of pneumonia. Proper maintenance and disinfection of these commercial water systems are necessary to prevent the bacteria from spreading.
Strategies for Healthy AC Use
Mitigating potential health drawbacks involves establishing practical usage and maintenance habits. Setting the thermostat to a reasonable level avoids the stress of extreme cold, with an ideal range often cited between 23–26°C (73–79°F). It is also helpful to ensure the temperature difference between indoor and outdoor environments does not exceed about 6–8°C (10–14°F) to minimize physical shock.
To maintain air quality and system function, several strategies should be employed:
- Set the thermostat to a reasonable level, ideally between 23–26°C (73–79°F).
- Limit the temperature difference between indoor and outdoor environments to no more than 6–8°C (10–14°F).
- Use a supplemental humidifier to maintain indoor relative humidity within the suggested 40% to 60% range.
- Change or clean air filters at least monthly to prevent the buildup and circulation of allergens.
- Schedule professional annual service to ensure coils and drain pans are clean and free of microbial growth.
- Adjust the unit’s vents to avoid direct, prolonged airflow onto the body, which reduces localized drying of the skin and eyes.