Staying healthy through winter comes down to a handful of habits that protect your body’s natural defenses and limit your exposure to circulating viruses. Cold weather itself doesn’t make you sick, but it creates conditions that do: dry indoor air, more time spent in enclosed spaces with other people, and a measurable drop in your nose’s ability to fight off infections. Here’s what actually works.
Why Cold Air Weakens Your First Line of Defense
Your nose is warmer than the air you breathe in winter, and that temperature difference matters more than most people realize. Cells lining your airway mount a stronger antiviral response at core body temperature (37°C) than at the cooler temperature inside your nasal passages (around 33°C). Research published in PNAS found that the immune sensors in airway cells work roughly 65% more efficiently at the warmer temperature, which means cold, dry air flowing through your nose gives viruses like rhinovirus a window to replicate before your immune system can shut them down.
This is one reason scarves and face coverings aren’t just about comfort. Warming and humidifying the air before it enters your nose helps maintain that first line of defense. It’s also why so many winter colds start with a scratchy throat or runny nose: the virus gains a foothold in the cooler upper airway before the body can respond.
Keep Indoor Humidity Between 40 and 60 Percent
Heated indoor air in winter often drops below 30% relative humidity, which is bad news for two reasons. Dry air lets virus-carrying droplets shrink and float longer, increasing your chance of inhaling them. It also dries out the mucous membranes in your nose and throat, weakening the physical barrier that traps pathogens.
An MIT study published in the Journal of the Royal Society Interface found that maintaining indoor relative humidity between 40 and 60 percent was associated with lower rates of respiratory infections and deaths. Regions that fell outside that range, either too dry or too humid, consistently saw worse outcomes. A simple hygrometer (under $15 at most hardware stores) lets you monitor levels, and a humidifier can bring a dry room back into range. Just clean it regularly so it doesn’t become a source of mold.
Sleep Is Non-Negotiable
People who chronically get less than seven hours of sleep per night are three times as likely to develop a common cold compared to those who get eight hours or more. That’s not a small increase in risk. Sleep is when your body produces and distributes key immune cells, and cutting it short leaves you measurably more vulnerable.
If you’re doing everything else right but consistently sleeping six hours, you’re undermining all of it. Prioritize a consistent bedtime, keep screens out of the last 30 minutes before sleep, and keep your bedroom cool. These basics matter more during cold and flu season than any supplement.
Wash Your Hands for 20 Seconds
Respiratory viruses land on surfaces constantly. Influenza can remain infectious on stainless steel for up to 24 hours, and some coronaviruses survive on hard surfaces for several hours after drying. Every doorknob, light switch, and phone screen is a potential transfer point to your face.
The CDC recommends scrubbing your hands with soap and water for at least 20 seconds, which removes significantly more viral particles than shorter washes. The mechanical action of rubbing, combined with soap breaking down the fatty outer layer of enveloped viruses like flu and COVID-19, is what does the work. Hand sanitizer with at least 60% alcohol is a reasonable backup when soap isn’t available, but soap and water is more effective overall. The habit that matters most: wash before eating and after returning home from public spaces.
Move Your Body, but Don’t Overdo It
Moderate exercise strengthens immune surveillance, improves the function of immune cells, and reduces the chronic low-grade inflammation that makes infections harder to fight. Public health guidelines recommend 150 to 300 minutes of moderate-intensity activity per week, and this range consistently shows the most balanced immune benefits.
The catch is that extreme or prolonged high-intensity exercise can temporarily suppress immune function for anywhere from 3 to 72 hours afterward, creating a window of increased susceptibility to infection. A brisk walk, a cycling session, or a moderate-paced run all count. Training for an ultramarathon in January without careful recovery planning is a different story. If you’re already feeling run down, a lighter workout is smarter than pushing through.
Vitamin D and Zinc: What the Evidence Supports
Vitamin D levels drop in winter because you’re getting less sunlight, and lower levels are independently associated with a higher incidence of respiratory infections. A large meta-analysis found that daily vitamin D supplementation between 400 and 1,200 IU per day during fall, winter, and spring slightly but significantly reduced the risk of respiratory infections. The key word is “daily.” Large, infrequent mega-doses did not show the same benefit. Most over-the-counter vitamin D supplements fall within this effective range.
Zinc is a different tool with a different purpose. It doesn’t prevent colds, but if you start taking zinc acetate lozenges within the first 24 hours of symptoms, the evidence is striking: high-dose zinc lozenges (80 to 92 mg of elemental zinc per day, dissolved in the mouth every two to three hours while awake) shortened cold duration by about three days on average. That’s nearly half the typical length of a cold. The lozenges need to dissolve slowly in your mouth, not be swallowed whole, because the zinc needs direct contact with throat tissue. Common side effects include a metallic taste and mild nausea.
Improve the Air You Breathe Indoors
You spend the majority of winter hours indoors, often in rooms with poor ventilation. Opening a window for even 10 minutes creates meaningful air exchange that dilutes viral particles. When that’s not practical, portable HEPA air purifiers make a real difference. CDC testing in a standard conference room found that two HEPA air cleaners reduced exposure to simulated exhaled aerosol particles by up to 65%. When shopping for one, look for a clean air delivery rate (CADR) that matches your room size, which is typically listed on the box.
Ventilation matters most in shared spaces: offices, classrooms, living rooms where your household gathers. Even upgrading your home HVAC filter to a higher-rated option (MERV 13 or above) captures more airborne particles during normal operation.
Stay Current on Vaccines
Annual flu vaccination remains one of the most effective ways to avoid the worst winter illness. For the 2025-2026 season, updated COVID-19 vaccines are recommended on an individual decision-making basis for everyone six months and older, with the strongest recommendation for adults 65 and older and those with conditions that increase the risk of severe disease. If you haven’t had a flu shot or updated COVID vaccine heading into winter, both can be given at the same visit at most pharmacies.
RSV vaccines are also now available for adults 60 and older and for pregnant individuals (to protect newborns). These three respiratory viruses account for the vast majority of serious winter illness, and vaccination reduces both your personal risk and the amount of virus circulating in your community.
Putting It All Together
No single habit makes you bulletproof. The people who get through winter without getting sick tend to stack several layers of protection: they sleep enough, keep their indoor air from drying out, wash their hands consistently, stay active at a moderate level, and keep their vaccines current. None of these require dramatic lifestyle changes. Most of them cost nothing. The key is consistency from November through March, when respiratory viruses peak and your body’s defenses are working hardest.