Why cold air can narrow breathing tubes
The airways do more than carry air: they warm and moisten it before it reaches the lungs. In cold, dry conditions, that job pulls heat and moisture from the airway lining. In people with reactive airways, this change can trigger the smooth muscles wrapped around the breathing tubes to contract. The tubes’ inner opening becomes smaller, increasing resistance to airflow.
This is bronchoconstriction—temporary tightening of the muscles around the airways. It is not that cold air freezes the tubes or makes them shrink like material cooling in a freezer. Rather, the airway responds to the stress of conditioning cold, dry air.
Why shoveling can make it worse
Physical effort raises the body’s demand for oxygen, so breathing speeds up and moves more air through the lungs. During strenuous activity, people may also breathe through the mouth, bypassing some of the warming and humidifying that happens in the nose. The airways must handle a larger flow of cold, dry air just as the muscles may be primed to tighten.
The narrowed passages can make breathing feel harder and may bring on coughing, wheezing, or chest tightness. Cold air and exertion can combine: faster breathing increases the airway’s exposure, while reactive airway muscles reduce the room available for airflow.
