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 seem to catch whatever is going round.
The difference between you usually comes down to a handful of plain things. Most of them are within your reach, 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. Healthy adults catch two to four colds a year, more in a hard winter. Young children catch six to eight or more, 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. The immune response also slows with age, so after about sixty the habits below count for more.
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, nurses, and anyone who spends the day in a crowded office or on packed trains meet far more of them than someone who works alone. Your colleague's secret may simply be a house without children.
Cold viruses travel mostly on hands and in the air. The average person touches their face about twenty times an hour, and nearly half of those touches land on the nose, mouth 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. Where there's no sink, an alcohol hand gel removes cold viruses from the hands at least as well as soap and water. So does fresh air: a room with a window open carries far fewer viruses than a sealed one with a dozen people breathing the same air.
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. When healthy adults were given a cold virus on purpose, the ones who had been sleeping less than six hours a night were about four times as likely to come down with the cold as those sleeping seven or more. A short week of sleep before a busy season is an open door.
Long stress lowers the defences
The same holds for stress, and the longer it lasts, the more it matters. People under heavy, ongoing pressure, the kind that runs for a month or more, such as trouble at work or a strained relationship, catch colds more readily when exposed, and the risk climbs with the level of stress. A hard season does far more damage than a bad day.
People protect you in an unexpected way
This one surprises people. Those whose lives include many kinds of relationship, such as family, friends, colleagues, neighbours, a club or a church, catch fewer colds when exposed to a virus than people with only one or two kinds of connection, even though they meet more people. Nobody knows why for certain, 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
People who do moderate exercise on most days spend about 40 percent fewer days with colds than those who barely move, and their colds are milder. Walking briskly, cycling, swimming and similar steady activity all count. The one exception is punishing training: marathon runners and people who push hard for long periods often catch more infections in the days after big efforts, so rest days earn their place.
Cold showers have a following of their own, helped along by Wim Hof. People who ended their usual hot shower with half a minute or more of cold water took about 29 percent fewer sick days off work in the months that followed, but they caught colds just as often. The cold seems to change how people cope while they're ill more than whether they get ill.
Food and your gut
A large share of your immune system sits along the gut, and what you feed it shows up there. Healthy adults who ate several servings of live fermented foods a day, such as yoghurt, kefir and sauerkraut, ended up with a wider range of gut bacteria and lower markers of inflammation within a few weeks.
Carnivore and keto eaters often say they catch fewer colds since changing how they eat. There's a plausible reason: high blood sugar dulls the immune cells that fight infection, which is part of why people with poorly controlled diabetes pick up more infections, and both diets keep blood sugar low and steady. Nobody has yet counted colds on these diets against others, so for now it rests on what people report.
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. Smoking slows them down, which is why smokers catch more infections and keep them longer. Heavy drinking weakens the defences too. Dry indoor air in winter dries the lining out, and a bowl of water on the radiator or a can help. Aim for indoor humidity of around 40 to 60 percent, which a cheap hygrometer will show you: flu virus coughed into a dry room stays infectious far longer than in air with some moisture in it.
Your mother was half right about the scarf. A virus gives you a cold, and cold air on its own gives you nothing, but winter stacks several things in the virus's favour. The inside of your nose runs cooler in cold weather, and at that temperature its antiviral defence works less well. 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
Low vitamin D goes with more chest and throat infections. Correcting a real shortfall, usually with vitamin D3, the form your skin makes and the one that raises levels best, lowers that risk, and the people who gain the most are the ones who were most deficient to begin with. If your colds cluster in winter and you spend most of the day indoors, a vitamin D test is worth having, and an makes it easy to do.
Vitamin C has a smaller role than its reputation. Taking it regularly makes colds a little shorter, but it prevents them only in people under extreme physical strain, such as marathon runners or soldiers training in the cold. Starting it once a cold has begun does little. Zinc lozenges started at the first sign may shorten a cold a little, though that's far from settled. 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 in large doses.
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 last as long as the pollen, dust or pet hair does, which can mean weeks. A cold usually clears within 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 help too: they clear a blocked nose faster than cold ones, hot chicken soup faster still, and in the lab chicken soup showed a mild anti-inflammatory effect, which makes a mug of bone broth a sensible choice as well. Colds spread most easily in the first few days, when the symptoms are at their worst, and you can pass one on until they've gone, so staying home for those worst days keeps your cold off the next desk.
Salt water is worth a try at the first sign. Rinsing the nose with a and saline packets dissolved in boiled and cooled water, never straight from the tap, and gargling salt water a few times a day may shorten a cold by a day or two and make it less likely to spread at home, though that still needs confirming.
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, because hard exercise with a fever puts real strain on the heart.
When it needs checking
Most colds are better within one to two weeks, longer in young children, and a cough can hang on for a few weeks after the rest has cleared. Get checked if a cold is no better 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 anyone whose infections have become more frequent alongside other changes in their 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
Nobody avoids every cold, and trying to is a recipe for anxiety. 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: How One Sleepless Night Puts Your Health at Risk — what a short night does to the immune cells that fight infection, and how to protect your sleep in a busy season.
Wondering whether your vitamin D is low? Nutrient Deficiencies: Who's at Risk and Which Test to Get — who tends to run low on vitamin D, iron and B12, and which test settles it.
Know someone who catches every cold going? Send them this. It might save them another round of ginger shots.
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.
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