Society. Air conditioning: can it be dangerous for your health?

Air conditioning doesn't make you sick per se, but it can contribute to certain health problems, especially when used improperly. How can you enjoy the cool air conditioning without the discomfort? Here's the answer from pulmonologist Frédéric le Guillou, president of the French Respiratory Health Association.
Used well, air conditioning significantly improves comfort during periods of extreme heat. But in certain conditions, it can also become a source of discomfort or respiratory problems, particularly in vulnerable people.
Colds, headaches, conjunctivitis and other allergy symptoms: what if it's the air conditioning?One of the first adverse effects is dry air. By lowering ambient humidity, air conditioning dries out the mucous membranes in the nose, throat, and eyes, which can lead to irritation, a dry cough, or discomfort, which can lead to tonsillitis and other colds.
Another common pitfall: excessively large temperature differences between the outdoors and air-conditioned spaces. These thermal shocks can cause headaches, chills, or muscle tension, particularly in the neck and back.
In extreme cases, very significant temperature fluctuations can cause sudden vasoconstriction. This reaction of the vascular system can, in some people, lead to faintness or even loss of consciousness. However, cardiac arrest is extremely rare in this context.
The need for regular maintenanceThe quality of the air diffused also depends on the condition of the system. "If the filters are not cleaned regularly," warns Dr. le Guillou, They can accumulate dust, mold, or bacteria, which are then dispersed into the indoor air. In rare cases, certain infections such as Legionnaires' disease have been linked to poorly maintained air conditioning systems.
Legionnaires' disease is a lung infection caused by a bacterium called Legionella pneumophila which can develop in poorly maintained air conditioning systems, particularly in cooling towers (those using water, such as in hospitals, etc.). When dispersed in the air in the form of fine droplets, it can be inhaled, causing often severe pneumonia.
In general, insufficient ventilation in enclosed spaces can also promote the circulation of viruses.
Additionally, some appliances can concentrate allergens or re-suspend them, circulating the air in poorly ventilated rooms. Dust, dust mites, mold spores, and pet hair—these indoor pollutants can trigger or worsen allergic reactions.
Some people are indeed more sensitive to the effects of air conditioning.
"This is the case for those whose mucous membranes are fragile, particularly in cases of allergies, asthma or sinusitis," recalls the pulmonologist. Dry air or airborne allergens can exacerbate their symptoms. A weakened immune system also makes one more vulnerable to infectious agents that can be carried by a poorly maintained device. People with chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD), or those sensitive to temperature variations, are also more exposed to adverse effects.
Finally, children and the elderly, due to their less efficient thermal regulation or the fragility of their mucous membranes, are particularly reactive to an atmosphere that is too cold. Prolonged exposure to poorly regulated air conditioning, especially without sufficient hydration, can aggravate these reactions.
Adjust the temperature of your air conditioning correctlyTo limit the adverse effects linked to air conditioning, a few simple measures can be put in place:
– the indoor temperature must remain moderate, with an ideal difference of 5 to 7°C compared to the outside, never more than 10°C;
– the flow of cold air should be directed towards the ceiling rather than directly onto people;
– use filters with good health performance (e.g. HEPA) as mentioned by the Ministry of Health;
– regular maintenance of the system is essential: the filters must be changed and cleaned frequently to avoid the accumulation of dust or microorganisms.
– UFC Que Choisir recommends dusting the air vents with soapy water. Although there is no inspection or maintenance contract requirement for consumer air conditioners (only those with a power rating above 12 kW or units containing more than 4 kg of refrigerant are affected), it is recommended that you have your system (excluding portable air conditioners) checked by a professional every two years;
– good ventilation is also necessary to avoid air stagnation and reduce the risk of viral transmission;
– operate the appliance on “all fresh air”, and not on “partial or total air recycling”;
– it is also recommended to drink regularly to compensate for the dryness caused by dry air.
In summary, "air conditioning does not directly cause illnesses," reassures Dr. Frédéric le Guillou, But certain factors such as poor maintenance, overly dry air or individual sensitivity can cause various symptoms. People with allergies, asthma or respiratory problems should be extra vigilant, as they are more susceptible to them.
Please note : an order from the ministers responsible for construction and energy defines the conditions for regulating cooling systems . In premises where a cooling system is installed, it must only be put into operation or kept in operation when the internal temperature of the premises exceeds 26°C.
To learn more about people vulnerable to air quality: Respiratory Health France
Source : Interview with Dr. Frédéric le Guillou, president of the association Santé Réspiratoire France (July 2, 2025); UFC Que Choisir (accessed July 2, 2025); Santé.gouv.fr (accessed July 2, 2025)
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