It’s winter and respiratory illnesses are everywhere. Will going out underdressed in cold weather make me sick?
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Version 0 of 1. To develop cold symptoms, you need to be infected by a virus. There’s a reason that happens more in winter – and the answer hangs indoors, in the air Read more in the Antiviral series It was inevitable that I would, as Oscar Wilde quipped, become like my mother. After decades of being told to “Put on more clothes! You’ll catch a cold!” I now, despite knowing better, insist the same for my daughter. “Another layer!” I demand of my partner, who begrudgingly bundles up a toddler already as puffy as the Michelin Man. The scientifically literate part of my brain understands that no jacket will shield her from the onslaught of daycare viruses. And yet I cling to the conviction that underdressing or stepping out the door with wet hair in winter must be avoided at all costs. Are the cries about catching one’s death just old wives’ tales passed down like family heirlooms, or is there a hint of truth in the warnings? Old wives’ tale or hint of truth? “People get more colds when the weather is cold,” says Hassan Vally, an associate professor of epidemiology at Deakin University. “It’s a very natural thing for humans to look for patterns,” he adds, but points out that correlation is not causation. “You’re not going to catch a cold by just going out in the cold,” says Dr Larisa Labzin of the University of Queensland’s Institute for Molecular Bioscience. To develop cold symptoms, you need to be infected by a virus, whether that be one of the rhinoviruses, coronaviruses, adenoviruses, respiratory syncytial virus or any other of the more than 200 strains that cause the common cold. Though the flu may present with similar symptoms, influenza viruses can cause much more severe disease. Labzin says the weather does have a substantial impact on the spread of these viruses. “Humidity really drops a lot in the winter – it gets really dry, your skin gets really dry – and that actually helps the viruses.” Moisture in the air hinders the airborne transmission of viruses, which means if “there’s low humidity and someone around you has the flu, it is going to transmit better at a further distance”, Labzin says. Respiratory illnesses peak in winter in temperate regions but Vally points out that the tropics – where temperatures vary less year-round – don’t experience the same seasonal spikes. The rainy season in many tropical areas has been linked to greater activity of influenza and RSV – which may seem counterintuitive as ambient humidity is higher then. One hypothesis that may explain both winter epidemics in temperate regions and rainy season outbreaks in the tropics is behavioural: people spend more time indoors to avoid the cold and wet. “Cooler temperatures certainly encourage people to gather indoors which increases transmission,” Prof Nathan Bartlett of the University of Newcastle says. A cold day keeps us inside for about one to two hours more on average, and rainy weather 30 minutes more, according to one estimate. Colder temperatures and immunity Though being cold won’t necessarily result in catching a cold, there is evidence that chillier temperatures affect immunity, Vally says. “Not only is there more opportunity to catch a virus, but our immune response is also a bit diminished,” Labzin agrees. “Cooler, dryer air allows viruses to be transmitted more efficiently and suppresses innate immune defences in the nasal passages – which is where these viruses get in,” Bartlett says. In dry winter weather, the mucus lining our airways – which plays an important role in trapping noxious inhaled substances – becomes thicker, making it more difficult for hair-like cells in the airways to remove trapped particles and pathogens. Less exposure to sunlight – necessary for our skin to produce vitamin D – in the colder months may also have an impact on immunity. “There is evidence that vitamin D deficiency is a risk factor for increased respiratory infections during winter,” Bartlett says. While a systematic review – the strongest form of scientific evidence – has found vitamin D supplements can help protect against respiratory infections, other findings suggest that supplementation is “unlikely to have a clinically relevant effect” in Australia, given that severe deficiency is not common here. Cold exposure can also be a physical stressor. “Whenever your body is under stress you can get transient suppression of your immune responses,” Vally says. “If you’re in -20C without a coat, your body is going to be hugely stressed, just like it would be hugely stressed if it ran a marathon.” Paradoxically, some small studies have found the stress of repeated cold water exposure activates the immune system slightly, suggesting the bodies of habitual winter swimmers develop adaptive changes. Ultimately, catching a cold results from a “complex interaction between virus, host and environment”, Bartlett says. “All three are in a constant state of flux – and winter coincides with changes in all of these factors.” How to avoid winter lurgies “For flu, for Covid, there are obviously vaccines available,” Labzin says, noting that an RSV jab is now recommended for immunocompromised groups. “The best protection … is getting vaccinated.” Flu vaccination rates in Australia, across all age groups, are significantly down from 2020 figures. “It’s important for people to not take antibiotics for a viral infection, because antibiotics won’t do anything,” Labzin says, citing the growing issue of antimicrobial resistance. Minimising transmission by practising good hygiene, wearing a respirator mask and staying home while sick is familiar to most from the Covid pandemic – and the same advice applies to the common cold. Donna Lu is an assistant news editor at Guardian Australia Antiviral is a fortnightly column that interrogates the evidence behind the health headlines and factchecks popular wellness claims What health trend do you want examined? Your contact details are helpful so we can contact you for more information. They will only be seen by the Guardian. Your contact details are helpful so we can contact you for more information. They will only be seen by the Guardian. |