Staying healthy comes down to a handful of habits that strengthen your immune system and reduce your exposure to viruses and bacteria. No single strategy is bulletproof, but layering several together makes a meaningful difference, especially during cold and flu season. Here’s what actually works, backed by the strongest available evidence.
Sleep Is Your Immune System’s Foundation
If you’re cutting corners on sleep, your body’s first line of defense takes a hit almost immediately. Restricting sleep to just four hours for a single night reduces natural killer cell activity to about 72% of normal levels. Natural killer cells are the immune cells that detect and destroy virus-infected cells before an infection can take hold, so even one rough night leaves you more vulnerable.
The sweet spot for most adults is seven to nine hours per night. Consistency matters too. Going to bed and waking up at roughly the same time helps your body regulate the immune processes that ramp up during deep sleep. If you’re heading into a season when everyone around you is sick, prioritizing sleep is one of the simplest and most effective things you can do.
Exercise Helps, but Overdoing It Backfires
Regular moderate exercise strengthens immune function compared to a sedentary lifestyle. But the relationship between exercise and immunity follows what researchers call a J-shaped curve: moderate activity lowers your risk of upper respiratory infections, while prolonged high-intensity training actually suppresses your immune system.
After an intense workout, your body enters a window of transient immunosuppression where T cells and natural killer cells function below normal. This vulnerable period can last anywhere from 3 to 72 hours, depending on how hard and how long you pushed. During that window, you’re more susceptible to picking up whatever virus is circulating.
The practical takeaway: keep most sessions under 60 minutes at a moderate pace. Think brisk walking, cycling, swimming, or jogging at a conversational effort. Save the high-intensity work for when you’re well rested and not already fighting off early symptoms. If you feel something coming on, a light walk is fine, but a grueling interval session could tip the scales in the virus’s favor.
Chronic Stress Quietly Weakens Your Defenses
When you’re stressed for days or weeks at a time, your body pumps out elevated levels of cortisol and other stress hormones. These hormones directly interfere with T cells, the immune cells responsible for recognizing and attacking specific pathogens. Stress hormones alter the structural proteins inside T cells, impairing their ability to activate and migrate to infection sites. Cortisol also reduces the number of immune cells circulating in your bloodstream, leaving fewer defenders available when a virus shows up.
You can’t eliminate stress entirely, but you can blunt its immune effects. Regular physical activity (at moderate intensity), adequate sleep, and even brief daily practices like deep breathing or time outdoors help lower baseline cortisol. The goal isn’t perfection. It’s avoiding the sustained, unmanaged stress that keeps your immune system in a chronically suppressed state.
Feed Your Gut to Support Immunity
About 70% of your immune tissue sits in and around your digestive tract, which means what you eat has a direct effect on how well you fight off infections. A large meta-analysis of probiotic supplementation in non-elderly adults found that people taking probiotics reduced their risk of experiencing at least one respiratory infection by 9%. More notably, the total number of sick days dropped by 23%, and both the duration and severity of infections decreased significantly.
You don’t necessarily need a supplement to get these benefits. Fermented foods like yogurt, kefir, kimchi, sauerkraut, and miso deliver live beneficial bacteria naturally. Pairing them with prebiotic fiber from vegetables, fruits, whole grains, and legumes feeds those bacteria once they arrive in your gut. A diet heavy in processed food and low in fiber does the opposite, starving the microbial communities your immune system depends on.
Zinc Can Shorten a Cold if You Act Fast
Zinc lozenges are one of the few over-the-counter remedies with solid evidence behind them, but timing and dose matter. Across seven randomized trials, zinc acetate and zinc gluconate lozenges delivering more than 75 mg of elemental zinc per day shortened cold duration by an average of 33%. That’s roughly two to three fewer days of symptoms.
The catch is that you need to start within the first 24 hours of feeling symptoms, and you need to take multiple lozenges throughout the day to hit the effective dose. Zinc works locally in the throat by interfering with viral replication, so lozenges are more effective than pills you swallow. At doses of 80 to 92 mg per day for one to two weeks, serious side effects are unlikely, though some people experience nausea or a metallic taste.
Improve the Air You Breathe Indoors
Most respiratory viruses spread through tiny airborne particles that accumulate in poorly ventilated spaces. The CDC recommends aiming for five or more air changes per hour to meaningfully reduce viral particles indoors. Increasing from two to five air changes per hour substantially cuts the time it takes to clear contaminated air from a room.
In a home setting, you can work toward this target by opening windows on opposite sides of a room to create cross-ventilation, running bathroom or kitchen exhaust fans, and using a portable air purifier with a HEPA filter. The filtration from an air purifier counts toward your total air changes, so even in a sealed apartment during winter, a properly sized HEPA unit makes a real difference. This matters most when someone in your household is already sick, or when you’re hosting guests during peak flu season.
Masks Still Work When You Need Them
In high-risk situations like a crowded airplane, a hospital waiting room, or close contact with a sick family member, wearing a well-fitted mask reduces the number of viral particles you inhale. N95 respirators filter out roughly 54% of ambient aerosol particles even under real-world conditions (which include small gaps around the edges), and higher-rated masks perform better still. Fit is critical: a loose mask of any type lets unfiltered air leak in around the sides, drastically reducing its effectiveness. Pressing the nose wire firmly and choosing a mask that seals against your cheeks makes more difference than the mask’s rated filtration alone.
Stay Current on Vaccines
Vaccines remain the most targeted way to prevent specific infections. The current adult immunization schedule recommends an annual flu shot for all adults, along with an updated COVID-19 vaccine (one dose for most adults, two for those 65 and older). RSV vaccines are now recommended for adults 50 and older in certain circumstances, and pneumococcal vaccines are advised based on age and risk factors.
These vaccines don’t just reduce your chance of getting infected. They also lower the severity and duration of illness if you do catch something, which means fewer days in bed and a lower risk of complications like pneumonia. Getting vaccinated before peak season (typically by late October for flu and COVID) gives your body time to build protection.
Basic Hygiene Still Matters
Hand hygiene prevents the fecal-oral and touch-based transmission routes that airborne precautions miss. Many stomach bugs and some respiratory viruses spread when you touch a contaminated surface and then touch your face, which most people do 15 to 20 times per hour without realizing it. Washing your hands with soap and water for 20 seconds, especially before eating and after being in public spaces, interrupts that chain. Alcohol-based hand sanitizer (at least 60% alcohol) works as a backup when soap isn’t available, though it’s less effective against certain viruses like norovirus.
Keeping your hands away from your eyes, nose, and mouth is arguably just as important as washing them. Those are the entry points viruses use most often, and reducing contact with your face limits opportunities for infection even when your hands aren’t perfectly clean.