It's your fourth cold since October. The colleague at the next desk has been in every day, eats worse than you, and claims never to catch anything. You've tried the vitamin C, the ginger shots and the extra layer, and you still keep getting sick.
The difference between you usually comes down to a handful of plain things. You can change most of them, and one of them has nothing to do with your body at all.
How often is normal
Start with the numbers, because they're reassuring. A healthy adult catches two or three colds a year, more in a hard winter. Young children catch six to eight, and a lot of that comes home with them. So four colds in a season, if you share a house with a toddler or a classroom's worth of viruses, is ordinary. What matters is the direction: more than you used to get, colds that drag on for weeks, or infections that need treatment again and again. Older adults come down with symptoms more often, as immunity declines with age, so the habits below count for more with every decade.
Why one cold doesn't protect you from the next
Get over measles and you're usually protected for life. Get over a cold and you're protected from that one cold, which helps far less than it sounds. Well over 200 virus types can cause a cold. Rhinoviruses, behind at least half of them, come in at least 165 types of their own, each with a slightly different coat. The defences you built against last month's virus barely recognise this month's. So catching four a year says more about how many viruses you meet than about your immune system.
Protection does pile up, though, one type at a time. When 991 children in Tucson were followed from birth, those in large day-care groups, with six or more other children, had frequent colds at about twice the odds at the age of two. From six to eleven they had them less often than children kept at home, and by thirteen the difference was gone. That slow collecting is a likely reason grown-ups catch fewer colds than toddlers.
The biggest factor is who's around you
The single biggest predictor of how many colds you catch is how many viruses you meet. Parents of small children, teachers and nurses, or a day in a crowded office or on packed trains, all mean far more of them than working alone. Your colleague's secret may be a house without children.
A base in the Antarctic shows how much comes down to people. Twelve men wintered at a British station on Adelaide Island, completely cut off. After 17 weeks without a single visitor, six of them came down with a cold, one after another. No virus was ever found. The likeliest source was a contaminated object or a man carrying the virus without symptoms, and not the husky dogs that shared the station. Even at the bottom of the world, the cold came from people and the things they handle.
Cold viruses travel mostly on hands and in the air. When medical students were filmed in a lecture, they touched their faces 23 times an hour, and 44 percent of those touches landed on the mouth, nose or eyes, the doors a cold virus uses. Washing your hands when you get home and before you eat, and keeping your fingers away from your face, cuts the number that reach you. Away from a tap, reach for an alcohol gel. On hands smeared with a cold virus, the gel removed it better than soap and water did.
In one test, the air mattered more than the hands. Men given a cold in the lab played cards for 12 hours with healthy men. Some of the healthy players had their arms restrained so they couldn't touch their faces, and 10 of 18 caught the cold anyway, close to the 12 of 18 among those free to touch. In another round, the cards and other things that eight sick men had handled for 12 hours went to 12 healthy men, and none of them caught it. So fresh air counts too. An open window thins out whatever a roomful of people is breathing out.
Flying fits the same picture. When 1,100 passengers flying from San Francisco to Denver were followed up a week later, about one in five reported a cold, on planes that recirculated their cabin air and on planes that used only fresh air alike. On a plane, the people in the rows around you count for more than the air system.
When someone at home is ill, give them their own towel, keep a window open in the room they're in, and wash your hands after looking after them.
Sleep decides whether a virus takes hold
Meeting a virus is one thing. Whether it takes hold depends on the state you're in when it arrives, and sleep is the biggest lever you have.
In one test, 164 healthy adults wore a sleep monitor on the wrist for a week and then took a cold virus as nose drops. Sleepers on less than six hours caught the cold at over four times the rate of those getting more than seven. From six hours up to seven, there was no extra risk at all. A short week of sleep before a busy season is an open door. The Sleep-Immune Connection, linked below, shows what one short night does.
Stress that drags on
The same holds for stress, and the length of it matters more than the size. When 276 volunteers were exposed to a cold virus through the nose, a severe upset lasting less than a month made no difference. Trouble lasting a month or more did, and it was mostly two kinds: being out of work or short of it, and a long-running conflict with family or friends. A hard season counts for much more than one bad day.
People protect you in an unexpected way
In another of these cold-virus tests, volunteers counted how many kinds of relationship they had, out of twelve: partner, parent, friend, workmate, neighbour, a club or a church, and so on. Then came the cold virus. Volunteers with only one to three kinds of tie caught the cold about four times as often as those with six or more. They made more mucus, cleared their noses less well and shed more virus, even though the well-connected meet more people and more germs. Why it works isn't fully known, though lower stress and better sleep probably play a part. Loneliness is a risk for your body as well as your mood.
Movement cuts your sick days
When 1,002 adults were followed through an autumn and winter, those who did aerobic exercise five or more days a week had 43 percent fewer days with cold symptoms than those who barely moved, and their colds were milder. Walking briskly, cycling, swimming and similar steady activity all count.
The exception is punishing effort. In the two weeks after a 56-kilometre race in Cape Town, a third of the runners came down with cold symptoms, twice as many as people who hadn't run, and the fastest runners caught the most. Rest days earn their place.
Cold showers have a following of their own. When 3,018 Dutch adults ended their usual hot shower with 30 to 90 seconds of cold water, they took 29 percent fewer sick days off work over the next three months, though the number of days they felt ill stayed the same. The cold seems to change how people cope while they're ill more than whether they get ill.
Food and your gut
Immune cells are built from protein and run on zinc, iron and vitamin A. Meat, fish, eggs, shellfish and liver carry every one of them in forms the body absorbs far more easily than the plant versions. A plate built on those covers the raw materials before any pill comes into it. Why You Can't Boost Your Immune System (and Shouldn't) has the food side in full.
Blood sugar matters too. High glucose slows the white cells that track down germs: they move less well, swallow fewer bacteria and kill fewer of the ones they catch. That's part of why poorly controlled diabetes brings more infections. Carnivore and keto keep blood sugar low and steady, which is a plausible reason colds might come less often on them. Colds haven't yet been counted on these diets against others, so for now it stays a reasonable guess.
A large share of your immune system sits along the gut, and fermented foods are a useful side. In a small test, healthy adults who worked up to several servings a day of yoghurt, kefir, sauerkraut and other live foods ended up with a wider range of gut bacteria and lower inflammation markers over a few months.
Winter, and what wears the lining down
Your nose and airways are lined with tiny hairs that sweep viruses and dust out before they settle. Cigarette smoke shortens them, and in tests where the cold virus went straight into the nose, smokers caught the cold more often than non-smokers.
Dry indoor air in winter dries the lining out as well, and a bowl of water on the radiator or a can help. Aim for indoor humidity of around 40 to 50 percent, which a cheap hygrometer will show you. When flu virus was coughed into a room with dry air, about three-quarters of it was still infectious an hour later. Above 43 percent humidity, only about a fifth was.
The illness is far older than its name. Its symptoms and treatment already appear in the Ebers papyrus from Egypt, the oldest medical text that survives, written before 1500 BC. "Cold" only came into use in the 16th century, because the symptoms looked like the effects of cold weather.
Your mother was half right about the scarf. A virus gives you a cold, and a chill on its own can't make one. It may tip one into showing, though. When 180 healthy volunteers were tested, half sat with their feet in a bowl of cold water. Over the next four or five days, 13 of those 90 reported a cold, against 5 of the 90 whose feet stayed dry. Winter also stacks several things in the virus's favour.
Rhinoviruses grow best at about 33 to 35°C, the temperature inside your nose, and breathing cold air cools it further. In mouse airway cells grown in the lab, the antiviral defence worked less well at that cooler temperature. People crowd together indoors with the windows shut. And with the sun too low to make vitamin D for months at a time, levels fall just as colds rise. A scarf over your nose on a freezing day is less daft than it looks.
Vitamin D, and the limits of the other pills
Running low on vitamin D brings more infections of the chest and throat. Across 25 tests covering over 11,000 people, vitamin D taken daily or weekly cut the risk of those infections, and those who started out lowest gained the most. Big occasional top-ups did nothing. Vitamin D3, the form your skin makes, raises levels better than D2. If your colds cluster in winter and you spend most of the day indoors, a vitamin D test is worth having. Why Every Nutrient Deficiency Checklist Says You're Low, linked below, covers who tends to run low and which test settles it.
Vitamin C has a smaller role than its reputation. Taken every day, it made no difference to how many colds people caught, except for marathon runners, skiers and soldiers training in the subarctic, whose colds halved. It shortened adults' colds by about 8 percent, and starting it once a cold had begun showed no consistent effect.
Zinc did little to stop colds in a 2024 review, and whether lozenges shorten one is still uncertain. Other antioxidant pills, from vitamin E to quercetin, do little for colds. Your immune cells make oxidants on purpose to kill the virus, so antioxidants are better eaten in food than swallowed as pills.
Is it a cold at all
Some "constant colds" are something else. Allergies bring sneezing, a runny nose and congestion without a fever, often with itchy eyes and throat, and they hang on for as long as the pollen, dust or pet hair is around, which can mean weeks. A cold is normally gone in a week or two. If yours never seem to finish, or they follow the seasons like clockwork, allergy is worth ruling in or out.
Flu is the other look-alike, and the difference shows in how it arrives. A cold creeps in over two or three days, stays mostly in your nose and throat, and lets you carry on. Flu hits within hours, aches through your whole body, and leaves you too exhausted to carry on at all.
Once you've caught one
Rest is the unglamorous fix, and it works. Sleep more than usual, drink enough to keep your throat comfortable, and let the cold run its course. Hot drinks are worth having. In a small test, sipping hot water sped up the flow of mucus out of the nose, hot chicken soup sped it up more, and cold water slowed it down. In a lab dish, chicken soup also held back the white cells that drive the stuffiness, a mild anti-inflammatory effect, which makes a mug of a sensible choice as well. You can pass a cold on until the symptoms have gone, so staying home while they're at their worst keeps your cold off the next desk.
Salt water is worth a try at the first sign. In a small test, adults who rinsed their noses and gargled with salt water got over their colds about two days sooner and passed them on to fewer people at home, though that still needs a larger test to confirm. A makes the rinse easy, with saline packets dissolved in water that's been boiled and cooled, never straight from the tap. For the gargle, stir good-quality unrefined salt, with nothing added, into warm water.
Antibiotics do nothing for a cold, because colds are caused by viruses and antibiotics only work on bacteria. Green or yellow mucus is a normal stage of a cold as it runs its course, and its colour alone says little about whether bacteria are involved.
If you want to move, use the neck check. When the symptoms sit above the neck, a runny nose or a scratchy throat, a gentle walk or an easy session is usually fine. Once they reach below it, with a fever, aching muscles or a tight chest, rest until they've passed. A fever already pushes your heart rate up, and hard exercise piles more on top.
When it needs checking
Colds usually clear in seven to ten days, longer in young children, and a cough can hang on for a few weeks after the rest has cleared. Get checked if a cold hasn't improved after ten days, or if a cough lasts more than three weeks.
Frequent colds in a healthy adult are almost always about exposure, sleep and stress. A few patterns need proper attention: infections that need antibiotics several times a year, pneumonia more than once, infections that keep coming back in the same place, or illness with fevers, night sweats or weight loss without an obvious reason. The same goes for infections that have become more frequent alongside other changes in your health. Those are signs to get checked, because they can point to something underneath, from diabetes to a problem with the immune system itself.
Stack the odds
Avoiding every cold is impossible, and chasing it only feeds the worry. What you can do is stack the odds: sleep enough, keep long stress in check, stay connected to people, move most days, keep your vitamin D where it should be, and wash your hands when you come home. Your colleague may just be lucky with their household. You can make your own luck with the rest, and next winter the count might stop at two.
Tonight, go to bed early enough to get seven hours, and do the same for the next week.
Short on sleep and catching everything going? The Sleep-Immune Connection: What One Sleepless Night Does to Your Defences — what a short night does to your infection-fighting cells, and how to guard your sleep in a busy season.
Wondering whether your vitamin D is low? Why Every Nutrient Deficiency Checklist Says You're Low — who tends to run low on vitamin D, iron and B12, and which test settles it.
Know someone who catches every cold going? Pass this on. It might spare them another round of ginger shots.
Tried something here, or got a question it didn't answer? Write to us at contact@allforlife.club. Your questions shape the next articles.
Disclaimer: This article is general information. For advice about your own health or medication, talk to a qualified health professional. If you notice any of the warning signs described above, or your infections are becoming more frequent, get checked.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
Sources
Wikipedia. Common cold. en.wikipedia.org
Wikipedia. Measles. en.wikipedia.org
Wikipedia. Rhinovirus. en.wikipedia.org
Ball TM, Holberg CJ, Aldous MB, et al. (2002). Influence of attendance at day care on the common cold from birth through 13 years of age. Archives of Pediatrics & Adolescent Medicine 156(2):121–126. doi.org/10.1001/archpedi.156.2.121
Allen TR, Bradburne AF, Stott EJ, et al. (1973). An outbreak of common colds at an Antarctic base after seventeen weeks of complete isolation. The Journal of Hygiene 71(4):657–667. doi.org/10.1017/s0022172400022920
Kwok YL, Gralton J, McLaws ML (2015). Face touching: a frequent habit that has implications for hand hygiene. American Journal of Infection Control 43(2):112–114. doi.org/10.1016/j.ajic.2014.10.015
Turner RB, Fuls JL, Rodgers ND (2010). Effectiveness of hand sanitizers with and without organic acids for removal of rhinovirus from hands. Antimicrobial Agents and Chemotherapy 54(3):1363–1364. doi.org/10.1128/AAC.01498-09
Dick EC, Jennings LC, Mink KA, et al. (1987). Aerosol Transmission of Rhinovirus Colds. Journal of Infectious Diseases 156(3):442–448. doi.org/10.1093/infdis/156.3.442
Zitter JN, Mazonson PD, Miller DP, et al. (2002). Aircraft cabin air recirculation and symptoms of the common cold. JAMA 288(4):483–486. doi.org/10.1001/jama.288.4.483
Prather AA, Janicki-Deverts D, Hall MH, Cohen S (2015). Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep 38(9):1353–1359. doi.org/10.5665/sleep.4968
Cohen S, Frank E, Doyle WJ, et al. (1998). Types of stressors that increase susceptibility to the common cold in healthy adults. Health Psychology 17(3):214–223. doi.org/10.1037/0278-6133.17.3.214
Cohen S, Doyle WJ, Skoner DP, et al. (1997). Social Ties and Susceptibility to the Common Cold. JAMA 277(24):1940–1944. doi.org/10.1001/jama.1997.03540480040036
Nieman DC, Henson DA, Austin MD, Sha W (2011). Upper respiratory tract infection is reduced in physically fit and active adults. British Journal of Sports Medicine 45(12):987–992. doi.org/10.1136/bjsm.2010.077875
Peters EM, Bateman ED (1983). Ultramarathon running and upper respiratory tract infections. An epidemiological survey. South African Medical Journal 64(15):582–584. pubmed.ncbi.nlm.nih.gov/6623247
Buijze GA, Sierevelt IN, van der Heijden BC, et al. (2016). The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial. PLoS One 11(9):e0161749. doi.org/10.1371/journal.pone.0161749
Jafar N, Edriss H, Nugent K (2016). The Effect of Short-Term Hyperglycemia on the Innate Immune System. The American Journal of the Medical Sciences 351(2):201–211. doi.org/10.1016/j.amjms.2015.11.011
Wastyk HC, Fragiadakis GK, Perelman D, et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell 184(16):4137–4153. doi.org/10.1016/j.cell.2021.06.019
Wikipedia. Mucociliary clearance. en.wikipedia.org
Cohen S, Tyrrell DA, Russell MA, et al. (1993). Smoking, alcohol consumption, and susceptibility to the common cold. American Journal of Public Health 83(9):1277–1283. doi.org/10.2105/AJPH.83.9.1277
Noti JD, Blachere FM, McMillen CM, et al. (2013). High humidity leads to loss of infectious influenza virus from simulated coughs. PLoS One 8(2):e57485. doi.org/10.1371/journal.pone.0057485
Johnson C, Eccles R (2005). Acute cooling of the feet and the onset of common cold symptoms. Family Practice 22(6):608–613. doi.org/10.1093/fampra/cmi072
Foxman EF, Storer JA, Fitzgerald ME, et al. (2015). Temperature-dependent innate defense against the common cold virus limits viral replication at warm temperature in mouse airway cells. Proceedings of the National Academy of Sciences 112(3):827–832. doi.org/10.1073/pnas.1411030112
Martineau AR, Jolliffe DA, Hooper RL, et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 356:i6583. doi.org/10.1136/bmj.i6583
Tripkovic L, Lambert H, Hart K, et al. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. The American Journal of Clinical Nutrition 95(6):1357–1364. doi.org/10.3945/ajcn.111.031070
Hemilä H, Chalker E (2013). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2013(1):CD000980. doi.org/10.1002/14651858.CD000980.pub4
Nault D, Machingo TA, Shipper AG, et al. (2024). Zinc for prevention and treatment of the common cold. Cochrane Database of Systematic Reviews 2024(5):CD014914. doi.org/10.1002/14651858.CD014914.pub2
NHS. Common cold. nhs.uk
Saketkhoo K, Januszkiewicz A, Sackner MA (1978). Effects of drinking hot water, cold water, and chicken soup on nasal mucus velocity and nasal airflow resistance. Chest 74(4):408–410. doi.org/10.1378/chest.74.4.408
Rennard BO, Ertl RF, Gossman GL, et al. (2000). Chicken soup inhibits neutrophil chemotaxis in vitro. Chest 118(4):1150–1157. doi.org/10.1378/chest.118.4.1150
Ramalingam S, Graham C, Dove J, et al. (2019). A pilot, open labelled, randomised controlled trial of hypertonic saline nasal irrigation and gargling for the common cold. Scientific Reports 9(1):1015. doi.org/10.1038/s41598-018-37703-3