Has it ever happened to you that you go out in biting cold, nail a good session, and then the next day your throat feels weird or your nose starts running? In that moment the conclusion feels obvious: “I got cold, so I’m getting sick.” It’s an automatic thought because two events happen close together. The problem is we often blame the wrong culprit. Let’s look at what science says and, more importantly, what actually makes sense in practice.
Why we get sick more often in winter
To catch a cold or the flu you have to encounter a pathogen, most often a virus. Cold weather doesn’t “create” illness out of nothing. What it can do, though, is put you in less-than-ideal conditions: more irritated airways, harder recovery, and habits that expose you more.
In winter it’s not just the temperature that changes. The context changes, and we end up in an environment that helps viruses spread:
- More time indoors and closer contact. At school, at work, on public transport, and in poorly ventilated spaces, close contact happens more often. That makes it easier for viruses to circulate.
- Drier air and easier viral spread. When it’s cold outside, the air holds less water vapor. Then we heat homes and offices, raising temperature without adding moisture, so the air gets even drier and relative humidity often drops. In these conditions some viruses, especially influenza, tend to survive and transmit more easily.
- Drier mucous membranes and less efficient local defenses. Your airways act like a filter thanks to mucus and tiny cilia. When the air is dry, mucus tends to dehydrate and the nose’s natural “cleaning” system works worse. Result: it’s harder to trap and clear particles and pathogens, and your airways can be more vulnerable.
- Vasoconstriction in the nose. In cold conditions, blood vessels in the nose narrow to conserve heat. That means a bit less blood reaches the mucosa. When that “supply” drops, local defenses can be slower to react.
- Less sun and lower vitamin D. In the colder months, at our latitudes, producing vitamin D from sunlight becomes harder. If levels drop a lot, immunity can also take a hit.
When training in the cold can genuinely increase risk
Cold by itself isn’t the main issue. Risk goes up when several stress factors stack on top of each other.
High training load with poor recovery. Long and intense sessions, especially when repeated without enough recovery, are associated in some contexts with more upper respiratory symptoms/infections. This is the well-known “J-curve” hypothesis: moderate training may be protective, too much can increase risk (but that doesn’t mean “intensity makes you sick”).
Low energy availability. In winter, if you cut your food intake too much, do frequent “fasted” sessions without a clear reason, or don’t hydrate properly, you increase stress on the body. That doesn’t automatically make you sick, but it can make you less resilient.
Airways irritated by cold, dry air. Some research suggests cold exposure can weaken local immune responses in the nose, which is one of the first lines of defense. A paper in the Journal of Allergy and Clinical Immunology describes how lower temperatures may reduce antiviral mechanisms mediated by the nasal epithelium.
Proper clothing. If you go out underdressed and stay cold for a long time, or you get home soaked and take too long to change, you’re simply increasing physiological stress and lowering recovery quality. You don’t “catch” a virus from the cold. The cold can reduce local defenses and raise overall stress, making it easier for a virus you’ve already been exposed to to take hold.
Below roughly -10°C, especially with strong wind, the game changes. Now it’s about safety: higher risk of hypothermia and frostbite, but also respiratory and cardiovascular stress, especially if you push intensity or have risk factors.
Practical rules to train in the cold without paying for it
Before and during
- Warm-up is essential to prepare muscles and joints and to raise core temperature gradually. Make it longer than usual. If you feel stiff in the first 10 minutes, don’t force it. Give your body time to “switch on.”
- Avoid long stops. If you stop for photos, traffic lights, a repair, or a chat, keep moving at low intensity whenever you can. Standing still while sweaty in the cold is the trap.
- Protect hands and feet, because they’re often the weak link that drives stress up unnecessarily.
- If the air is very cold and dry, covering mouth and nose with a neck gaiter can reduce irritation, especially on lower-intensity sections.
After the session
- The golden rule is simple: don’t stay wet. Change and dry off as soon as possible, especially if you need to drive, wait, or stand around.
- Sleep quality is a priority, especially after a hard session: that’s when you recover, lock in adaptations, and bring the immune system back into balance.
Nutrition
- Avoid being in a constant deficit. When intensity goes up, bring carbs during training and take recovery after the session seriously, because energy and recovery matter for your defenses too.
- Hydration: drink even if you’re not thirsty. In winter thirst is less “loud,” but you still lose fluids: by breathing cold, dry air, by sweating (even if you notice it less), and because cold increases urine output. Hot drinks help, even just because they make it easier to drink regularly.
What to do if symptoms show up
Full stop
- If you have fever, chills, widespread aches, or heavy fatigue, the choice is simple: no training today.
- If symptoms move into your chest and you feel shortness of breath, tightness, or chest pain, stop and get medical assessment, without waiting for it to “go away.”
You can consider a very easy session
- If symptoms stay mild and “up top” (a bit of nasal congestion, a slightly irritated throat), with no fever and good energy, you can do something, but with one rule: very easy and very short. If during the session you feel worse, your head feels “closed,” or fatigue spikes, stop and call it a day.
Smart return
- Wait until the main symptoms are truly gone. Then restart with one or two easy days just to get the engine running again, and only then reintroduce intensity gradually.
- Don’t try to “make up” missed workouts with double sessions or hard sessions too close together. That’s the fastest way to relapse.