The cold from the air conditioner makes you ill by itself

A cold is a viral infection. More than 200 different viruses can cause it, with rhinovirus being the most common culprit, according to the CDC. No stream of cold air can create a virus out of nothing: if there is no virus around you, the air conditioner can make you feel bad, but it cannot infect you.

That is also why cold-storage workers do not fall ill constantly, and why the summer cold from the AC largely coincides with summer virus waves, when we all gather in closed cooled rooms and exchange viruses at a two-metre distance.

Because it contains a grain of truth, discovered quite recently. A study in the Journal of Allergy and Clinical Immunology (Huang et al., 2023) shows that when the temperature inside the nose drops by about 5 degrees, local antiviral defence weakens noticeably: the secretion of protective extracellular vesicles falls by nearly 42%, and viral replication doubles. The same mechanism explains why colds are seasonal.

In other words: cold does not create the illness, but it unlocks the door for the virus. An air conditioner blowing directly at your face for hours creates exactly such local cooling of the nasal mucosa.

The cold stream is not the only side of the question. Air conditioners dry the air, and a dry mucosa is more permeable to viruses. Dirty filters in turn spread dust, mould and allergens around the room, provoking coughs and runny noses easily mistaken for a cold. These are real effects, but again they are not an infection, only a favourable environment for one.

The difference between outdoor and indoor temperature should be moderate: around 23-25 degrees in the room is enough for comfort. The stream should not point directly at people, filters should be cleaned regularly, and the air in the room should not be allowed to become dry. And of course: if the colleague next to you is sneezing, airing the room helps more than switching off the AC.

Our verdict: the claim is a MYTH, but with an important nuance. Colds are caused by viruses, not by cold. A cold and dry stream, however, weakens the nose's defences and makes infection easier. So do not be afraid of the air conditioner: set it sensibly and keep its filters clean.

The information in this article has been verified and is based on: the CDC page on the common cold and its more than 200 causes, the study by Huang et al. on the effect of cold on nasal antiviral immunity (Journal of Allergy and Clinical Immunology, 2023) and the Harvard Health overview of viral rhinitis.