The Truth About Cold Weather and Getting Sick

In 2025, Australia recorded more than 427,000 laboratory-confirmed influenza notifications — around 21% more than the year before, and likely the highest number since flu became nationally notifiable back in 2001, according to analyses presented by the Australian Centre for Disease Control at the Doherty Institute's influenza symposium. And that's just the flu cases confirmed by a lab test. It doesn't count the millions of coughs, sniffles and sore throats that never make it into a statistic — the ones you nurse on the couch with a box of tissues and a Netflix queue.

Numbers like that always spark the same conversation around the office kitchen or the school pick-up line: "It's the cold weather, isn't it?"

It's one of the most enduring beliefs in Australian households. Your nan told you to put a jumper on or you'd catch your death. Your mum told you never to leave the house with wet hair. Someone at work insists they got sick because the air conditioning was "blasting" all afternoon. The belief is so baked into how we talk about illness that we literally named the illness after the temperature — a cold.

But here's the thing: the relationship between cold weather and getting sick is far more interesting, and far more nuanced, than either "cold air makes you sick" or "that's just an old wives' tale." Both of those answers are wrong. The truth sits somewhere in the middle, and understanding it can genuinely change how you get through winter.

At NextClinic, we're an Australian telehealth service, and every winter we see the same surge — people needing medical certificates for sick leave, scripts for their asthma preventers, and advice on whether what they've got warrants a trip to the doctor. We've had a front-row seat to Australia's winter illness season for years, and we spend a lot of time answering exactly this question.

So in this article, we're going to unpack what the science actually says about cold weather sickness, bust the most stubborn winter health myths doing the rounds, explain why the common cold in Australia peaks when it does, and give you a practical, evidence-based toolkit to prevent winter illness this year. By the end, you'll know precisely which piece of your nan's advice to keep — and which to gently retire.

First, the non-negotiable fact: you can't catch a cold from cold air alone

Let's start with the bedrock of this whole topic, because everything else builds on it.

Colds are caused by viruses, not temperatures. There are more than 200 different viruses that can cause the common cold, with rhinoviruses being the most frequent culprit. Healthdirect Australia describes a cold as a viral infection of the upper respiratory tract affecting your nose and throat, and notes that Australian adults average two to four colds a year, while children can rack up as many as eight.

No virus, no cold. Full stop.

You could sit in a Tasmanian winter wind in a singlet, soaked through, for an hour — and if there's no rhinovirus, influenza virus, RSV or coronavirus anywhere near you, you will not develop a respiratory infection. You'll be miserable, you may well be hypothermic, but you won't have a cold.

This is the part your nan got wrong, and it's worth internalising because it changes where you focus your prevention efforts. The threat isn't the temperature outside. It's the virus that hitched a ride on a doorhandle, a shared keyboard, or the breath of the person coughing two seats away on the train.

So, case closed? Cold weather is entirely innocent?

Not quite. This is where it gets genuinely fascinating.

Why cold weather still deserves some of the blame

Cold weather doesn't create illness. But it does something arguably sneakier: it stacks the deck in the virus's favour. Think of it less as the criminal and more as the getaway driver.

Researchers writing in The Conversation put it neatly — cold weather acts as a "risk amplifier," creating conditions that help viruses survive, spread and get past your body's defences. Here's how that actually works.

1. Your nose's immune system genuinely works worse when it's cold

This is the discovery that changed the conversation. In December 2022, researchers at Mass Eye and Ear and Northeastern University published a study in the Journal of Allergy and Clinical Immunology identifying a previously unknown immune response inside the nose — a "swarm" of tiny extracellular vesicles released by nasal cells that act as decoys, binding to inhaled viruses before those viruses can attach to your cells.

The catch? That protective response becomes inhibited at colder temperatures. The researchers described it as the first biological mechanism explaining why colds, flu and COVID-19 spike in cooler months — going beyond the old "people are just indoors more" explanation.

In other words: cold air really does lower your front-line defences. Your nose is your first checkpoint, and cold weather partially closes it.

2. Dry air dries out your natural filter

Your airways are lined with mucus and microscopic hair-like cilia that constantly sweep trapped particles — including viruses — up and out. It's called mucociliary clearance, and it's brilliantly effective when it's working properly.

Winter attacks it from two directions. Cold outdoor air holds less moisture, and then we crank up the indoor heating, which dries the air out further. Dry air dries the lining of your nose and throat, reducing how well mucus does its job. When that conveyor belt slows down, viruses get more time to settle in and infect cells.

3. Viruses themselves last longer in cold, dry conditions

Many respiratory viruses — rhinovirus, influenza, SARS-CoV-2 — remain infectious for longer and replicate more efficiently in colder temperatures and lower humidity. Rhinoviruses in particular replicate more happily at around 33°C (roughly the temperature inside your nasal cavity on a chilly day) than at your core body temperature of 37°C. Cold air cools the inside of your nose, and you've essentially rolled out the welcome mat.

4. We all pile indoors together

The classic explanation still holds real weight. When it's cold and dark, we shut the windows, close the doors and gather in poorly ventilated rooms — offices, classrooms, pubs, buses, gyms. Crowded spaces with poor ventilation let virus-containing droplets and aerosols build up in the air, making transmission far more likely. Winter doesn't just weaken you; it introduces you to more viruses.

5. Less sunlight means less vitamin D

Shorter days and more time indoors mean less UV exposure and therefore lower vitamin D production in the skin. Vitamin D plays a role in regulating immune function, and low levels are associated with weaker immune responses. It's not a magic bullet — but it's another small tilt in the wrong direction.

6. And then there's the foot-in-icy-water study

Here's a curveball that keeps the debate alive. Researchers at Cardiff University's Common Cold Centre ran a study, published in the journal Family Practice, in which 180 volunteers either had their bare feet chilled in ice water for 20 minutes or sat with their feet in an empty bowl. Over the following four to five days, 29% of the chilled group developed cold symptoms, compared with 9% of the control group.

Important caveat: this doesn't mean cold water conjured a virus out of thin air. The leading interpretation is that chilling constricts blood vessels in the nose and throat, dampening local immune defences, which may allow a virus you were already harbouring — one you would have fought off silently — to bloom into a full-blown cold.

So your nan wasn't completely off base. She just had the mechanism back to front. Being cold doesn't give you the virus. It may make you worse at fighting the one you've already met.

The Australian angle: why our winter illness season is its own beast

Here's something Australians often overlook — we're not simply living out a Northern Hemisphere winter in reverse.

A "cold snap" in Cairns and a cold snap in Canberra are wildly different experiences, yet both regions see winter respiratory illness surges. Queensland, with its balmy 20-degree July days, still gets flu seasons. That's a strong hint that temperature alone isn't the driver — behaviour, humidity, indoor crowding and school terms all matter enormously.

Australia's flu season typically ramps up from around May and peaks between June and September. But 2025 threw out the rulebook. The Australian CDC's analysis found that influenza activity remained elevated well into spring, driven partly by the emergence of the influenza A(H3N2) subclade K virus. The same report recorded 977 influenza deaths in the first nine months of 2025.

Vaccination coverage, meanwhile, reached only around 31% — yet the protection was meaningful. Australian surveillance networks found that vaccinated people in 2025 were roughly 56% less likely to visit a GP with influenza and around 49% less likely to be hospitalised compared with unvaccinated people.

There's also a uniquely Australian wrinkle: we travel. Australians heading to Europe, North America or Asia during our summer walk straight into their peak flu season and frequently bring souvenirs home. The Australian Centre for Disease Control has flagged unusually high flu levels heading into recent seasons, which is exactly why "winter prevention" is increasingly a year-round conversation here.

Six winter health myths, sorted

Let's run the most persistent ones through the evidence filter.

Myth 1: "Going outside with wet hair gives you a cold." Wet hair is uncomfortable and makes you feel cold, but it doesn't manufacture a virus. That said — and this is where the Cardiff study earns its keep — getting genuinely chilled may temporarily dampen your nasal defences. Verdict: mostly myth, with a small asterisk. Dry your hair for comfort, not paranoia.

Myth 2: "Air conditioning makes you sick." Air con doesn't produce viruses. What it can do is dry the air out (drying your airways) and, in poorly maintained or recirculating systems, move air between people without adequate fresh-air exchange. The problem isn't the cold air — it's the ventilation and the humidity. Verdict: myth, with a legitimate underlying concern.

Myth 3: "Vitamin C will stop me getting sick." This is the big one. A landmark Cochrane review analysing trials of at least 0.2g/day found that regular vitamin C supplementation had no effect on how often people in the general population caught colds (29 trial comparisons, over 11,000 participants). It did produce a modest but consistent reduction in the duration of symptoms with regular ongoing supplementation. Interestingly, in five trials involving people under extreme physical stress — marathon runners, skiers, soldiers in subarctic conditions — vitamin C halved the risk of catching a cold. Verdict: it won't build you a force field, and starting it once you're already sniffly is unlikely to help much.

Myth 4: "Antibiotics will clear this up faster." Colds and flu are viral. Antibiotics kill bacteria. Taking them for a cold does nothing for you and actively contributes to antibiotic resistance, one of the biggest public health threats we face. Verdict: comprehensively busted. If you'd like to understand more about when medication is and isn't appropriate, our blog covers this in detail.

Myth 5: "The flu shot gives you the flu." The vaccines used in Australia's National Immunisation Program cannot cause influenza. The mild achiness or fatigue some people feel for a day or so is your immune system responding — which is the entire point. Verdict: busted.

Myth 6: "Sweating it out under three doonas will break the illness." Rest is genuinely valuable. Deliberately overheating yourself is not, and can lead to dehydration. Verdict: rest yes, sauna-under-the-blankets no.

Is it a cold, the flu, COVID, RSV — or hay fever?

Winter symptom confusion is real, and getting this right matters for how you treat it and whether you should stay home.

A cold usually creeps up gradually. Sore or scratchy throat first, then sneezing, a runny or blocked nose, maybe a mild cough. You feel below par but you can generally function. Healthdirect notes symptoms typically settle within 7 to 10 days.

The flu tends to arrive like a freight train. Sudden fever, chills, aching muscles, headache, exhaustion so profound that getting to the kettle feels like a project. As Healthdirect puts it plainly, the flu usually makes you feel much more unwell than a cold.

COVID-19 overlaps heavily with both and no longer follows a tidy winter pattern — testing is the only reliable way to distinguish it.

RSV is often dismissed as a childhood illness but causes significant illness in older adults and infants, and is now nationally monitored alongside flu and COVID.

And don't forget hay fever. Itchy eyes, itchy nose, sneezing fits, clear runny nose, no fever, and symptoms that flare in specific environments or at specific times of day. Australia's pollen seasons are long and unforgiving, and allergic rhinitis is very frequently misread as an endless cold.

Cold weather is also particularly rough on people with asthma. Colds, flu and viral infections are among the most common triggers for asthma flare-ups, and cold, dry air can itself provoke airway narrowing. If that's you, winter is the season to make sure your preventer is current and your action plan is up to date — something you can sort out through an online consultation without leaving home.

What actually works: your evidence-based winter defence plan

Now for the useful part. Here's where to spend your energy.

Get vaccinated. It remains the single highest-impact action. The flu vaccine is free under the National Immunisation Program for people aged 65 and over, Aboriginal and Torres Strait Islander people from six months of age, pregnant women, children aged six months to under five years, and people with certain medical conditions. Given the 2025 data on reduced GP visits and hospitalisations among vaccinated Australians, this one isn't close.

Wash your hands properly, and often. Not a token rinse — 20 seconds with soap, including between fingers and under nails. Rhinovirus spreads beautifully via hands and surfaces, then rides into your body when you touch your face. Which brings us to the second half: try to keep your hands away from your eyes, nose and mouth.

Open a window. This is the most underrated intervention in the whole list. Improving indoor ventilation dilutes virus-laden aerosols. Even ten minutes of cross-ventilation in a meeting room, classroom or living room makes a measurable difference. Yes, it's cold. Put a jumper on — you now know it won't give you a cold.

Manage indoor humidity. Maintaining adequate humidity during winter reduces transmission risk and stops your airways drying out. A humidifier, a bowl of water near the heater, or simply not running the heating at maximum all help.

Prioritise sleep — seriously. This is one of the most striking findings in the field. In a study led by UCSF researchers, volunteers were exposed to a cold virus under controlled conditions. Those who'd slept less than six hours a night in the preceding week were 4.2 times more likely to catch the cold than those getting more than seven hours. Sleep isn't a luxury add-on to your immune system. It is your immune system's maintenance window.

Eat and move like it matters. Regular moderate exercise supports immune function. A diet with plenty of vegetables, fruit, wholegrains and protein supplies the raw materials your immune cells need. And given reduced winter sun exposure, it's worth discussing vitamin D with a doctor — particularly if you work indoors, cover up for cultural or religious reasons, or have darker skin.

Stay home when you're sick. The most generous thing you can do for your colleagues is not share your virus with them. This is precisely why we built our online medical certificate service — so you can rest at home rather than dragging yourself into a crowded waiting room to prove you're unwell.

Consider a mask in high-risk settings. On a packed train during a bad flu week, or visiting someone immunocompromised, a well-fitting mask is a low-cost, low-effort layer.

When it's more than "just a cold"

Most colds resolve on their own within 7 to 10 days with rest, fluids and simple symptom relief. But please seek medical advice promptly if you experience:

• Difficulty breathing, shortness of breath or chest pain
• A fever that persists beyond a few days, or a very high fever
• Symptoms that improve and then suddenly worsen — a classic sign of secondary infection
• Coughing up blood, or severe, persistent headache
• Confusion, dizziness, or signs of dehydration
• Symptoms lasting well beyond two weeks
• Any significant illness if you're pregnant, over 65, immunocompromised, or managing a chronic condition like asthma, diabetes or heart disease

In an emergency, call 000. For general health advice at any hour, healthdirect on 1800 022 222 connects you with a registered nurse 24/7.

For everything in between, that's where we come in. Through NextClinic, you can consult an Australian-registered practitioner online, get a prescription sent to your pharmacy, obtain a specialist referral if you need one, and receive a medical certificate for work or study — all without sitting in a waiting room breathing recycled air alongside a dozen other unwell people. We think that's a genuinely better way to handle winter.

The bottom line

So, does cold weather make you sick? Here's the honest answer, in one paragraph:

Cold air cannot give you a cold, because colds are caused by viruses and nothing else. But cold weather is far from an innocent bystander. It suppresses the newly discovered immune defence inside your nose, dries out your airways so mucus can't sweep viruses away, helps viruses survive longer in the air, pushes us all indoors into crowded, poorly ventilated spaces, and cuts our vitamin D. Cold weather doesn't cause illness — it opens the door and holds it politely ajar. And with Australia recording over 427,000 flu notifications in 2025 alongside vaccination coverage of just 31%, that door is being used more than it should be.

The genuinely encouraging news is that almost every one of those mechanisms has a simple, cheap countermeasure. Vaccination. Handwashing. An open window. Seven-plus hours of sleep. Staying home when you're crook.

Here's our challenge to you: pick one strategy from this article and put it into practice this week. Just one. Book your flu vaccination. Open a window in the room where your family spends the evening. Set a bedtime alarm and actually respect it. Move the hand soap somewhere you'll see it. Small, consistent changes are what separate a winter of back-to-back sniffles from a winter you barely notice.

Then tell us about it. Drop a comment below and let us know which strategy you've chosen — and check back to tell us how it went. We'd genuinely love to hear which winter health myth you grew up believing, too. (We're taking bets on wet hair.)

And if this winter does catch up with you despite your best efforts, remember that you don't have to leave the couch to get proper care. We're here whenever you need us.

This article is general information only and is not a substitute for personalised medical advice. Please consult a healthcare professional about your individual circumstances.

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