If Coronavirus Thrive in Cold Noses, Then Keeping It Warm May Help

We often see the common cold and flu on the rise during the colder months. These respiratory viruses — coronavirus, rhinovirus, influenza virus, and respiratory syncytial virus — are classed as winter viruses that thrive in colder environments at around 33°C (91.4 °F) or lower.

Keep the nose warm, science recommends

As follows, winter viruses seem to replicate better in colder noses or airways. Why? A 2020 paper of Akiko Iwasaki, a professor of many titles at Yale University who has contributed immensely to the Covid-19 literature, published March 2020 in the Annual Review of Virology, explained three reasons:

1. The lipids of winter viruses — that form the viral envelope encasing its genes — are more stable and structurally rigid in the cold.
2. Breathing cold or dry air slows the clearance of mucous — that traps foreign particles like viruses and bacteria — in the airways.
3. The immune system in the nose and airways becomes less vigilant when cold, particularly the antiviral interferon responses. The immune system works best during a fever for good reasons, after all.

“It keeps my nose warmer, and I think it helps to keep the immune system operating properly.”

If colder noses and airways favor the activities of winter viruses, then the opposite could be true as well. As the review stated, “Conversely, keeping the nose warm during the winter might boost innate antiviral resistance to the common cold virus.” And further suggested “wearing a face mask to keep the nose warm and moist” as a means to lower the risk of respiratory infection during the winter (see table 2 below).

“I’m constantly wearing a scarf around my nose,” Prof. Iwasaki once said in The Boston Globe. “It keeps my nose warmer, and I think it helps to keep the immune system operating properly.”

Warmer air warms the nose

“When exhalations approximating at pulmonary capillary blood temperature are re-inhaled under facemasks and cloth face coverings, the temperature of the nasal cavity, oral cavity, pharyngeal cavity, and upper airways may equalize with core body temperature,” Deepak Gupta, MD, clinical assistant professor at Wayne State University, wrote in an editorial letter to Medical Hypothesis earlier this May.

Simply put, the body warms the exhaled air. With facemasks on, this exhaled warmer air is rebreathed. The nose and airways are then warmed, which makes lives difficult for winter viruses, including SARS-CoV-2.

“Personal “therapeutic” environments may get created under facemasks and cloth face coverings due to rebreathing of ~ 95°F “hot” and ~ 80% “humid” exhalations, which may constantly mitigate SARS-CoV-2 inside the nasal cavity, oral cavity, pharyngeal cavity, and upper airways,” Prof. Dr. Gupta added. “This hypothesis is based on the report by the Department of Homeland Security (DHS): Science and Technology which has stated that at 95°F temperature and 80% relative humidity, the half-life of SARS-CoV-2 is one hour,” he wrote in another editorial letter to the Journal of Pediatrics. The original SARS-1 also lost its infectivity rapidly in warm and humid conditions.

Simply put, the body warms the exhaled air. With facemasks on, this exhaled warmer air is rebreathed. The nose and airways are then warmed, which makes lives difficult for winter viruses, including SARS-CoV-2. But this is not to encourage breathing hot air, which could irritate the airways.

Short abstract and considerations

Masking keeps the nose and airways warm, which is not conducive to replicating winter viruses, including the novel coronavirus. This is because winter viruses are less stable while the immune system works better in warm and humid conditions. This theory, however, is derived from extrapolations of animal or cell culture studies, and has not been verified in humans for doing so would be unethical. Presently, the data is insufficient to gauge how much real-life differences do warm noses play in disease control.

Regardless, more robust epidemiological studies have confirmed that masking works. It prevents respiratory infections like Covid-19 at least in two ways: (1) reducing the viral load inhaled by an uninfected person and (2) preventing the dispersion of virus particles from an infected person. And keeping the nose and airways warm may be an added bonus of facemasks.