Sleeping with the Air Conditioner On: Can It Really Make You Sick?
During hot summer nights, air conditioning can make the difference between uninterrupted, restorative sleep and hours of sweating, discomfort and repeated awakenings. Many people, however, hesitate to leave it running because they fear waking up with a cold, a sore throat, nasal congestion or muscular stiffness. Air conditioning does not directly cause the common cold because colds are viral infections. It can, however, create conditions that irritate the nose, throat, eyes and airways, particularly when the temperature is excessively low, the air becomes too dry, the airflow is directed towards the body or the filters are poorly maintained. Cold air does not cause the common cold According to the CDC, a cold is an upper respiratory infection caused by any of more than 200 respiratory viruses, with rhinoviruses being the most frequent cause. A person must be exposed to one of these viruses to develop a cold. A low air-conditioning setting cannot generate the virus inside the body. It is nevertheless possible to wake up with a blocked nose, dry throat or cough without having an infection. These symptoms may result from dry air, direct exposure to the airflow, allergens or dust circulating in the room. Fever, significant malaise or symptoms that persist and progressively worsen should not automatically be blamed on the air conditioner. Why dry air can irritate the nose and throat Air conditioners remove moisture from the air as they cool it. This is helpful in a very humid environment, but excessive dryness may irritate the eyes, nasal passages, throat and skin. Scientific reviews have associated low indoor humidity with more frequent acute eye and airway symptoms and reduced mucociliary clearance, one of the respiratory system’s natural defence mechanisms (Wolkoff, 2024). Cold, dry air may also aggravate congestion, sneezing and a runny nose in people with allergic or non-allergic rhinitis. Feeling congested after sleeping with the air conditioner on may therefore be genuine without indicating a viral infection. The US Environmental Protection Agency generally recommends keeping indoor relative humidity between 30% and 50%. A simple humidity meter can show whether a bedroom is unusually dry or humid. Humidifiers should not be used indiscriminately because excessive moisture encourages mould and dust mites, while the humidifier itself requires meticulous cleaning. What is the right bedroom temperature? There is no single temperature that is ideal for everyone. Age, sleepwear, bedding, humidity, air movement and individual preferences all affect thermal comfort. ASHRAE notes that research has considered a broad range of approximately 17–28°C, demonstrating why one rigid target cannot apply to every person and climate. What is clearer is that excessive heat disrupts sleep. A recent systematic review found that higher temperatures were generally associated with poorer sleep quality and shorter sleep duration. During a Mediterranean summer, a setting of approximately 24–26°C may be a reasonable starting point for many adults, adjusted according to comfort. This is not a medical threshold. The aim is to keep the bedroom comfortably cool without causing shivering, numbness or the need for excessively heavy bedding. Should the air blow directly onto the body? Continuous cold airflow towards the face, neck or chest may intensify dryness and muscular discomfort. It is preferable to direct the vents upwards or away from the bed and use the swing, sleep or low-fan setting. Air conditioning does not cause muscular infection or inflammation. Prolonged exposure to a cold draught may nevertheless contribute to muscle tension and stiffness, particularly when the body remains in the same position for several hours. Why ventilation still matters Most domestic split air conditioners recirculate indoor air and do not automatically bring fresh outdoor air into the room. If a bedroom remains closed for many hours, carbon dioxide, odours and indoor pollutants may accumulate. When outdoor conditions permit, briefly ventilating the room before bedtime and again in the morning helps renew the air. If someone in the room has a respiratory infection, air conditioning does not replace appropriate ventilation or measures to reduce transmission. Why filters must be maintained Air-conditioning filters capture dust and airborne particles. When they are not cleaned or replaced according to the manufacturer’s instructions, system performance declines and more pollutants or allergens may recirculate. The CDC’s National Institute for Occupational Safety and Health recommends ensuring that filters are correctly sized, properly fitted and within their recommended service life. Filters in a domestic unit used daily should be inspected and cleaned as frequently as the manual specifies. Professional servicing is also important, particularly before the period of intensive summer use. An unpleasant smell, visible mould, leaking water or symptoms that consistently begin when the unit is switched on warrant technical inspection. Strong disinfectants should not be sprayed indiscriminately inside the unit because they may cause irritation or damage the equipment. How to sleep safely with air conditioning A moderate, stable temperature, no direct airflow onto the body, appropriate humidity, regular ventilation and clean filters provide the safest approach. Sleep mode or a timer can prevent excessive cooling towards dawn, when the outdoor temperature may also fall. People with asthma, severe allergies or chronic respiratory disease, as well as infants and older adults, may require more individualised conditions. Wheezing, breathing difficulty, persistent coughing, high fever or severe symptoms that do not improve after leaving the room require medical assessment. The bottom line Air conditioning does not directly cause the common cold. It may nevertheless trigger or aggravate dryness, congestion, irritation, allergy symptoms and muscular discomfort if the temperature is set too low, the airflow is directed towards the body or the system is poorly maintained. There is no need to choose between sleeping in extreme heat and turning the bedroom into a refrigerator. Appropriate settings, regular maintenance and adequate air renewal make it possible to sleep with the air conditioner on without fearing that it will make us sick. Read the full article















