Summary
This episode of What's That Rash explores the age-old question of whether cold weather actually causes the common cold. Host Tegan Taylor and Dr. Norman Swan trace the history of cold virus discovery, from Walter Cruz's filtered nasal secretions experiments to the establishment of Britain's Common Cold Research Unit. They explain that colds are caused by viruses, primarily rhinoviruses and coronaviruses, not by cold temperatures themselves. The discussion examines the multiple factors that make colds more common in winter, including viral survival in cold dry air, increased indoor crowding, and changes in nasal immunity. In cold dry weather, blood vessels in the nose constrict, depriving the nasal lining of immune cells and protective mucus, which may make people more susceptible to viral infection. The episode notes that while controlled laboratory studies of cold exposure show a slight upregulation of immune function, real-world cold weather creates conditions that impair the nose's first line of defense. The hosts conclude that cold weather does not directly cause colds since viruses are the causative agents, but cold conditions can make people more susceptible to catching a virus they encounter. The episode also includes a listener feedback segment about organic food safety and the new Human Exposome Project.
Key Points
- Colds are caused by viruses (rhinoviruses and coronaviruses), not by cold temperatures
- Cold weather may increase susceptibility to viral infection by constricting nasal blood vessels and drying out mucus membranes
- Viruses survive longer in cold dry air and people spend more time indoors in winter, increasing transmission
- Controlled lab studies show cold exposure may slightly upregulate immune function, but real-world conditions differ
- Cold symptoms can linger for up to three weeks even from mild viral infections
- The history of cold virus discovery traces back to Walter Cruz's filtered nasal secretion experiments
- Adults typically get 2-4 colds per year, with peak symptoms occurring 1-3 days after onset
Key Moments
Cold dry air impairs nasal immunity and first-line viral defense
In cold dry weather, blood vessels in the nose constrict, depriving the nasal lining of immune cells and protective mucus, making the nose more susceptible to viral infection.
"when you are outside in the cold, the blood vessels to the surface tissue inside your nose contract. So it's deprived of blood and therefore deprived of immune cells. And it also dries out, so it's deprived of mucus."
Rhinoviruses and coronaviruses as the true causes of common colds
The hosts explain that colds are caused by rhinoviruses and coronaviruses that spread through aerosol transmission, with adults typically getting two to four colds per year. Cold weather does not directly cause illness but creates conditions that increase susceptibility.
"Two main families of viruses are rhinoviruses and coronaviruses, the family which COVID-19 is part of. And they're highly contagious. They spread by aerosol, like many respiratory viruses."
Controlled cold exposure may slightly upregulate immune function
While controlled laboratory studies of cold exposure show a slight upregulation of immune function, real-world cold weather creates dry conditions that impair the nose's first line of defense against viruses.
"When they've done controlled experiments, usually in small numbers of people, they find the exposure to cold, say in an ice bath or a cold environment, particularly repeated exposure, does seem to increase the efficiency of your immune system."
