Our association between being cold and catching a cold stretches back hundreds of years and still runs strong today. As a child, did your parents ever tell you to “put on a coat or you’ll catch a cold”? A recent poll of over 1,000 parents showed that about half of them tell their children not to go outside with wet hair and discourage them from playing outside during winter to prevent them from catching a cold.1Preventing colds in children: Following the evidence?. National Poll on Children’s Health.https://mottpoll.org/reports/preventing-colds-children-following-evidence However, commonly held beliefs aren’t always true, so let’s see what published research has to say on this issue.
What does it take to catch a cold?
All you really need to catch a cold is exposure to enough of a cold-causing virus. Unfortunately for us, many kinds of viruses can cause colds, which is one reason we haven’t yet developed a cure for the common cold. These viruses include rhinoviruses (which cause most colds), coronaviruses, parainfluenza viruses, and adenoviruses, among others. Strictly speaking, cold exposure can’t make you sick with a cold; only a virus can do that.
Ok, but can cold exposure weaken our immune systems, making us more susceptible to virus infection?
Several studies have tested how our immune systems respond when we are in a cold environment (some were even performed in Antarctica!) with the overall conclusion that the immune system is not systemically weakened by cold exposure.2Castellani, J. W., M Brenner, I. K. & Rhind, S. G. Cold exposure: human immune responses and intracellular cytokine expression. Med. Sci. Sports Exerc. 34, 2013-2020 (2002).https://www.ncbi.nlm.nih.gov/pubmed/12471310 However, these studies took a big-picture view of the immune system and, even though we may feel the aches and pains of a common cold throughout our whole body, cold infections are limited to our nose and upper airway. Therefore, we must consider how these local immune defenses respond to cold exposure.
For decades, scientists have known that cold exposure causes blood vessels in the nose and upper airway to constrict, called vasoconstriction, directing warm blood to the body’s core to protect the vital organs. Surprisingly, you don’t have to stand out in a snowstorm for this vasoconstriction to happen. Mild cold exposure can induce it too. For example, researchers observed vasoconstriction when they had study participants soak their feet in cold water or applied cold air or ice to participants hands, feet, or backs.3Mudd, S. & Grant, S. B. Reactions to chilling of the body surface: experimental study of a possible mechanism for the excitation of infections of the pharynx and tonsils. J. Med. Res. 40, 53-101 (1919).https://www.ncbi.nlm.nih.gov/pubmed/199724804Eccles, R. Acute cooling of the body surface and the common cold. Rhinology 40, 109-114 (2002).https://www.ncbi.nlm.nih.gov/pubmed/12357708
So how does vasoconstriction affect my immune system?
Vasoconstriction in the nose and upper airway has two main effects:
1. It causes the local temperature to drop a few degrees by reducing the amount of warm blood flowing through the area.3Mudd, S. & Grant, S. B. Reactions to chilling of the body surface: experimental study of a possible mechanism for the excitation of infections of the pharynx and tonsils. J. Med. Res. 40, 53-101 (1919).https://www.ncbi.nlm.nih.gov/pubmed/199724804Eccles, R. Acute cooling of the body surface and the common cold. Rhinology 40, 109-114 (2002).https://www.ncbi.nlm.nih.gov/pubmed/12357708 Lower temperatures are proven to weaken our cell’s own defenses against virus infection.5Foxman, E. F. et al. Temperature-dependent innate defense against the common cold virus limits viral replication at warm temperature in mouse airway cells. Proc Natl Acad Sci USA 112, 827-832 (2015).https://www.ncbi.nlm.nih.gov/pubmed/255615426Foxman, E. F., Storer, J. A., Vanaja, K., Levchenko, A. & Iwasaki, A. Two interferon-independent double-stranded RNA-induced host defense strategies suppress the common cold virus at warm temperature. Proc Natl Acad Sci USA 113, 8496-8501 (2016).https://www.ncbi.nlm.nih.gov/pubmed/27402752 This is like removing some of the door and window locks from houses in a neighborhood. It makes them much easier to break into.
2. It is also thought to reduce the number of local immune cells patrolling the area for viral trespassers. These immune cells travel in the bloodstream, so when less blood passes through the nose and upper airway, fewer immune cells do too.4Eccles, R. Acute cooling of the body surface and the common cold. Rhinology 40, 109-114 (2002).https://www.ncbi.nlm.nih.gov/pubmed/12357708
This means that cold exposure could make the nose and upper airway a favorable place for a cold virus to infect.
If cold exposure weakens our immune systems, does it weaken cold viruses too?
Unfortunately, no. Rhinoviruses, which cause the majority of colds, replicate better at colder temperatures found in the nose than elsewhere in our bodies, which is one reason cold infections are limited to our respiratory tract.
Does all this mean that being cold can increase our risk of getting a cold?
From all of this research, the answer should be a solid yes, but this has been difficult to prove in laboratory experiments.
A few studies have chilled participants, then exposed them to virus and found that cold exposure doesn’t have any affect on the participants’ chances of catching a cold.4Eccles, R. Acute cooling of the body surface and the common cold. Rhinology 40, 109-114 (2002).https://www.ncbi.nlm.nih.gov/pubmed/123577087Douglas, R. C., Couch, R. B. & Lindergren, K. M. Cold doesn’t affect the “common cold” in study of rhinovirus infections. JAMA 199, 29-30 (1967).https://www.ncbi.nlm.nih.gov/pubmed/4289651 However, this doesn’t mean that cold exposure is irrelevant to developing a cold.
Surprisingly, about one third of people infected with a cold-causing virus don’t experience cold symptoms.4Eccles, R. Acute cooling of the body surface and the common cold. Rhinology 40, 109-114 (2002).https://www.ncbi.nlm.nih.gov/pubmed/123577088Tyrrell, D. A., Cohen, S. & Schlarb, J. E. Signs and symptoms in common colds. Epidemiol. Infect. 111, 143-156 (1993).https://www.ncbi.nlm.nih.gov/pubmed/83942409Ketler, A., Hall, C. E., Fox, J. P., Elveback, L. & Cooney, M. K. The virus watch program: a continuing surveillance of viral infections in metropolitan new york families. Am. J. Epidemiol. 90, 244-254 (1969).https://academic.oup.com/aje/article-abstract/90/3/244/215186?redirectedFrom=fulltext10Granados, A., Goodall, E. C., Luinstra, K., Smieja, M. & Mahony, J. Comparison of asymptomatic and symptomatic rhinovirus infections in university students: incidence, species diversity, and viral load. Diagn. Microbiol. Infect. Dis. 82, 292-296 (2015).https://www.ncbi.nlm.nih.gov/pubmed/25999242 These infections are called sub-clinical or asymptomatic because they can’t be detected unless you specifically look for the virus. Some scientists hypothesize that if an individual with a sub-clinical infection is exposed to cold, weakening their local immune defenses, the cold-causing virus could gain an advantage and develop into a clinical and symptomatic infection. This theory hasn’t been solidly proven (or disproven) yet, but there is some indirect evidence supporting it.
What is the evidence that cold temperatures can lead to cold symptoms?
Let’s go back to those studies I mentioned that show cold exposure causes vasoconstriction in the nose and upper airway. Some of these report that participants having frequent colds also had the most pronounced cases of vasoconstriction, sometimes lasting for hours after cold exposure.4Eccles, R. Acute cooling of the body surface and the common cold. Rhinology 40, 109-114 (2002).https://www.ncbi.nlm.nih.gov/pubmed/12357708 This would weaken their local immune defenses, perhaps more so than in other participants, which could give a sub-clinical infection a better chance to develop into a clinical infection.
To look at this a little more rigorously, another study had participants soak their feet in cold water for 20 minutes and noted how many developed colds in the next 4-5 days, compared to participants who didn’t soak their feet in cold water. More than twice as many cold-treated participants developed colds compared to the control group.11Johnson, C. & Eccles, R. Acute cooling of the feet and the onset of common cold symptoms. Fam. Pract. 22, 608-613 (2005).https://academic.oup.com/fampra/article/22/6/608/497956
Additionally, there is anecdotal evidence reporting high incidence of cold infections among athletes and military personnel who spend long periods of time in cold environments.12Brenner, I. K. et al. Immune changes in humans during cold exposure: effects of prior heating and exercise. J. Appl. Physiol. 87, 699-710 (1999).https://www.physiology.org/doi/full/10.1152/jappl.19220.127.116.119?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&
While none of these studies definitively prove the theory, they certainly add some credibility to it.
Overall, will being cold increase my chance of having a cold?
Right now, we don’t really know. The evidence we have suggests that cold exposure doesn’t increase your risk of catching a cold. However, if you have a sub-clinical infection, cold exposure could weaken the immune defenses in your nose and upper airway, allowing the infection to progress and develop symptoms. We won’t know if this is true or not until more research is done, but in the meantime, keeping warm during cold weather might not be a bad idea!
Want to read about tested ways to get over colds quickly? Let me know in the comments or through the contact page!