When cold weather arrives, many people notice a common physiological reaction: a runny nose. This natural response protects the body from environmental changes. Understanding this phenomenon involves recognizing the functions of the nasal passages and how they adapt to maintain respiratory health.
The Nose’s Role in Respiration
The nose plays a crucial role in conditioning the air we breathe before it reaches the lungs. As air enters the nasal cavity, it is warmed and humidified to body temperature and near 100% humidity. This process safeguards the lungs from irritation or damage that cold, dry air could cause.
The nasal passages achieve this conditioning through mucus and tiny hair-like structures called cilia. Mucus, a sticky substance produced by specialized glands, traps airborne particles, dust, and microorganisms. The cilia then work in a sweeping motion to move this debris-laden mucus toward the throat, where it can be swallowed and eliminated.
The Body’s Response to Cold Air
When exposed to cold, dry air, the nasal lining detects these changes, triggering increased mucus production. This surge in moisture helps to humidify the incoming air, preventing the respiratory tract from drying out. Immune cells within the nose, such as mast cells, can also stimulate the release of liquid to moisten the air.
Blood vessels within the nasal passages dilate, increasing blood flow to the area. This increased blood supply warms the cold air as it passes through the nose, ensuring it reaches the lungs at a suitable temperature. Expanded blood vessels can also lead to fluid leaking into the nasal passages, contributing to the runny nose.
These responses are involuntary reflexes mediated by the nervous system. Cold, dry air stimulates sensory nerves in the nose, which send signals to the brain. The brain then directs the nasal glands to produce more secretions and the blood vessels to expand, resulting in “cold-induced rhinitis” or “skier’s nose.”
Why This Happens: A Protective Mechanism
The runny nose in cold weather is a protective mechanism for the lower respiratory system. Cold, dry air can irritate the airways, causing them to narrow and making breathing difficult. This is relevant for individuals with pre-existing lung conditions, as cold air can worsen their symptoms.
By warming and humidifying the air, the nose reduces the impact of environmental conditions on the lungs. Increased mucus production also acts as a barrier, trapping more foreign particles and microorganisms before they can reach the lungs. This helps to maintain the health of the respiratory tract and reduces susceptibility to infections.