As the mercury climbs toward 35-degree Celsius, the hum of an air conditioner becomes the soundtrack of survival. Indians retreat into our chilled sanctuaries, seeking refuge from the sweltering humidity. But for many, that relief comes at a cost: a scratchy throat, a persistent sniffle, and a foggy head—the dreaded summer cold.
Is the AC actually making you sick, or is it just a coincidence? This World Health Day, Dr. Divya Gopal, additional director of internal medicine at Sir H.N. Reliance Foundation Hospital, and Dr. Nilesh Sonawane, consultant pulmonologist at Apollo Clinic, decode why our cooling systems sometimes turn into irritant machines.
The thermal shock
The most common cause of feeling sick from an AC isn`t a germ at all—it`s physics. When you move between the 35 degrees Celsius heat of a Mumbai or Pune afternoon and a 20 degrees Celsius office, your body undergoes a thermal shock.
Dr Gopal explains that your respiratory lining—the delicate mucous membrane inside your nose and throat—is built for gradual transitions, not sudden plunges. “When you step out of 35 degrees Celsius heat into a freezing 20 degrees Celsius office or car, your blood vessels in the nose go into a mini panic.
They first constrict to conserve heat and then dilate rapidly as your body tries to adjust. This is basically vasomotor rhinitis in action. The result? Your lining swells, extra mucus pours out, and you get a stuffy, runny nose without a single virus in sight. Over time, this repeated shock stresses the cilia—the tiny hair-like structures that sweep out dust and germs—making your respiratory tract inflamed and hyper-reactive,” she warns.
The humidity trap: Why dry air invites viruses
While we celebrate ACs for removing sticky humidity, they often go too far. A healthy nose thrives in 40–60 per cent humidity. AC units, however, can strip that moisture down to a bone-dry 20–30 per cent.
Dr Sonawane notes that this dry environment is responsible for the lion’s share of uncomfortable symptoms like sore throats and dry coughs. “Air conditioning systems are used to cool indoor spaces by removing heat and moisture. This dry environment is responsible for many uncomfortable symptoms. The colder you set your air conditioning, the more likely you are to increase dryness and irritation,” he explains.
Dr Gopal takes it a step further, describing the mucus in your nose as a security system. “When the air is dry, that mucus thickens or cracks, creating an easy landing strip for actual viruses. Suddenly, a mild virus that your body would normally flush out can settle in and multiply. Patients often find their symptoms vanish the moment they step back into the humid outside air—a clear sign the AC was the culprit,” she adds.
Maintenance versus microbes
If your symptoms include sneezing, fatigue, or a persistent cough, the culprit might not be the temperature, but the machine`s hygiene. Experts estimate that 30–40 per cent of summer cold cases are actually caused by what is growing inside the unit.
Dust, pollen, and moisture collect on filters and evaporator coils, turning them into what Gopal calls a cozy hotel for mould, fungi, and bacteria. “When the AC blows, it aerosolises these particles straight into your breathing zone. Mould spores trigger allergic-type inflammation that feels exactly like a cold. Temperature and dryness get the blame, but dirty maintenance turns your AC from a friend into a low-grade irritant machine,” she states.
Dr Sonawane agrees, emphasising, “Dirty filters recirculate dust and animal dander, which can lead to bronchospasm (a spasm of the bronchial muscles) in people with asthma or pre-existing respiratory conditions. While Legionella bacteria are rare in residential split AC systems, they can thrive in poorly maintained cooling towers of large offices or hotels.”
Finding the sweet spot
So, how do we stay cool without getting sick? The doctors agree on a safe delta—the maximum temperature difference between the indoors and outdoors.
1. The 8-10 degrees Celsius rule: Gopal recommends keeping the gap between indoor and outdoor temperatures to no more than 10 degrees Celsius. If it’s 40 degrees Celsius outside, don’t aim for 20 degrees Celsius immediately.2. The sweet spot: Both experts identify 24-26 degrees Celsius as the ideal range.
“Finding a temperature range of 24-26 degrees Celsius is far more appealing to most consumers and helps to create a balance between temperature and moisture in the air. Setting the AC here will offer comfort and greatly reduce the chances of irritating your throat,” says Dr Sonawane.
Doctor-approved strategies for a healthy summer
To prevent the AC from compromising your health, follow this checklist of expert approved tips:
1. Acclimatise gradually: Don`t blast it arctic-cold the moment you walk inside. Gopal suggests giving your body 30–60 minutes to acclimatise. If it’s exceptionally hot, start your AC at 28 degrees Celsius and slowly bring it down to the sweet spot.2. Hydrate internally and externally: Use these tips- Drink up: Sonawane emphasises drinking plenty of fluids to keep the throat moist and less prone to irritation.- Warm relief: If you already have an irritated throat, he suggests warm or hot liquids like soup and tea, which provide immediate relief to the mucous membranes.- The humidifier hack: Gopal suggests a small humidifier in the bedroom if the air feels too dry. Alternatively, inhaling steam can help re-humidify the airway directly.3. Master your night mode: Leaving the AC on a low setting all night is a recipe for a morning sore throat.- Use sleep mode: This allows for gradual temperature changes while you sleep.- The fan switch: Sonawane recommends using the AC to cool the room down initially, then switching to a ceiling fan or using a timer to prevent excessive cooling throughout the night.4. Break the cycle: Don`t live in a sealed box. Sonawane advises taking breaks from the AC and opening windows periodically to allow for cross-ventilation. This reduces the accumulation of indoor pollutants and recycled air containing dust and allergens.
5. Avoid direct blast: Position your workstation or bed so you aren`t sitting directly in front of the unit. Direct exposure to the cold stream can lead to localised irritation and even muscle spasms in the bronchial tubes for sensitive individuals.
Irritant or infection? How to tell the difference
It is critical to recognise whether you are suffering from a simple environmental irritant or an actual acute viral infection. Here is how the doctors differentiate the two:
AC irritation (vasomotor rhinitis):1. Typically manifests as a dry, acrid, or slightly scratchy throat.2. Symptoms often include a stuffy or runny nose that appears suddenly when entering a cold room.3. Symptoms usually vanish or significantly improve the moment you switch off the AC or step into humid air.4. Generally, lacks systemic symptoms like high fever or severe body aches.
Viral summer cold:1. Presents with classic infection markers: fever, muscle pain, and deep fatigue.2. Congestion and runny nose persist regardless of whether the AC is on or off.3. Symptoms typically linger for more than a week.4. May involve a productive cough or significant respiratory distress.
Dr Gopal suggests being vigilant when it comes to experiencing the above symptoms, “If symptoms linger more than a week or you get fever and body aches, come see your doctor; sometimes it really is a virus riding on top of the AC irritation.” Sonawane adds, “When used correctly, air conditioning will be able to provide comfort as well as prevent harm to one`s respiratory system. The primary goal should be to increase moisture and decrease the amount of dry air. Treat your AC right—clean the filters, mind the thermostat, and stay hydrated—and you can enjoy a cool summer without the tissue box.”
World Health Day 2026: Hidden link between air conditioning and your sore throat
