The single most effective everyday habit for avoiding illness is washing your hands properly. It cuts your risk of catching a cold by about 20% and reduces stomach bugs by 23% to 40%. But handwashing is just one layer of protection. Staying healthy through cold and flu season, and year-round, comes down to stacking several simple habits that each chip away at your exposure and strengthen your body’s ability to fight off infections.
Handwashing Still Comes First
Handwashing prevents roughly 30% of diarrhea-related illnesses and about 20% of respiratory infections like colds. For people with weakened immune systems, the benefit is even larger: proper handwashing reduces diarrheal illness by 58% in that group. In schools, regular handwashing cuts absenteeism from stomach bugs by 29% to 57%.
The technique matters more than people think. Use soap and water, scrub for at least 20 seconds (including under your nails and between your fingers), and focus on the moments that count most: before eating, after using the bathroom, after blowing your nose, and after being in a public space where you’ve touched shared surfaces like doorknobs, elevator buttons, or shopping carts.
When you can’t get to a sink, hand sanitizer with at least 60% alcohol is a reasonable backup. It does have blind spots, though. Soap and water are significantly better at removing norovirus (the most common cause of stomach flu), C. diff, and certain parasites. If your hands are visibly dirty or greasy, sanitizer won’t cut it.
Sleep Is Your Immune System’s Foundation
Skimping on sleep doesn’t just make you tired. It triggers a cascade of inflammation throughout your body. Research published in Cell found that prolonged sleep deprivation causes a buildup of a signaling molecule in the brain that then leaks into the bloodstream, flooding the body with immune cells called neutrophils and triggering a storm of inflammatory proteins. This isn’t a subtle effect. In animal studies, it produced inflammation severe enough to cause damage across multiple organs.
What this means practically: when you’re sleep-deprived, your immune system shifts into a state of chronic, unfocused inflammation instead of the precise, targeted response it needs to fight off a specific virus. You become both more inflamed and less protected. Most adults need seven to nine hours per night. During cold and flu season especially, consistent sleep is one of the highest-return investments you can make in staying healthy.
Keep Indoor Air at the Right Humidity
The air inside your home plays a bigger role than most people realize. Research funded by the National Science Foundation found that maintaining indoor relative humidity between 40% and 60% is associated with lower rates of respiratory infections and deaths. Regions in the study consistently saw fewer cases during periods when indoor humidity stayed in that range, while conditions above or below it were linked to worse outcomes.
This works through several mechanisms. Dry air (below 40%) lets viral particles stay suspended and infectious longer, and it dries out the mucous membranes in your nose and throat that serve as your first line of defense. Overly humid air (above 60%) promotes mold and dust mites, which can weaken respiratory health over time. A simple hygrometer (available for a few dollars) lets you monitor your indoor levels, and a humidifier or dehumidifier can bring them into range. In winter, when indoor heating dries the air dramatically, this is especially worth paying attention to.
Get Your Flu Shot (and Stay Current on Vaccines)
The seasonal flu vaccine remains one of the most straightforward ways to reduce your chances of serious illness. CDC data from the 2024-2025 flu season shows the vaccine reduced flu-related hospitalizations by 48% to 55% among working-age adults, and by 63% to 78% among children. Even in adults over 65, where immune responses tend to be weaker, effectiveness against hospitalization ranged from 38% to 57%.
The vaccine’s protection against milder outpatient illness is lower, typically in the 32% to 56% range depending on age group and the match between the vaccine and circulating strains. That means you can still catch the flu after being vaccinated, but you’re far less likely to end up in the hospital. Beyond flu shots, staying current on other recommended vaccines (COVID boosters, pneumonia vaccines for those who qualify, and routine childhood immunizations) closes off additional avenues for infection.
Masks Work When the Risk Is High
You don’t need to wear a mask to the grocery store year-round, but knowing when and how to use one gives you a powerful tool during outbreaks or when you’re in a particularly high-risk situation. N95 respirators are designed to achieve a tight facial seal and filter very small airborne particles efficiently. Standard surgical masks block splashes and larger droplets but leave gaps around the edges that allow tiny aerosolized particles through.
If you’re flying during flu season, visiting someone who’s immunocompromised, or navigating a crowded indoor space during a known outbreak, a well-fitted N95 or KN95 provides meaningfully better protection than a cloth or surgical mask. Fit is critical: an N95 with gaps around the nose bridge loses much of its advantage.
Exercise Helps, but Don’t Overdo It
Regular moderate exercise, things like brisk walking, cycling, or swimming, supports immune function and has been linked to reduced cold incidence. The benefit comes from consistent, moderate activity rather than intense training. Research in The American Journal of Medicine found that moderate-intensity exercise reduced common cold frequency, though it didn’t significantly change the total number of upper respiratory infection episodes overall.
The practical takeaway: regular movement keeps your immune system primed, but there’s no need to push into exhaustive workouts hoping for extra protection. In fact, very intense or prolonged exercise can temporarily suppress immune function in the hours afterward. Aim for 150 minutes per week of moderate activity, which is the same target recommended for heart health.
What About Vitamin D and Zinc?
Vitamin D supplements have been widely promoted for preventing respiratory infections, but the evidence has weakened as more data has come in. An updated meta-analysis published in The Lancet Diabetes & Endocrinology, covering over 61,000 participants across 40 studies, found that vitamin D supplementation did not produce a statistically significant reduction in the risk of acute respiratory infections. The overall effect was small enough that it could be due to chance. If you’re genuinely deficient in vitamin D (something a blood test can confirm), correcting that deficiency is still worthwhile for bone health and general well-being, but taking extra vitamin D specifically to prevent colds isn’t well supported.
Zinc lozenges are another popular cold remedy, and some studies suggest they may shorten cold duration if taken very early after symptoms start. However, according to the Mayo Clinic, there’s no consensus on the right dose, formulation, or treatment plan. The upper safe limit for adults is 40 mg of zinc per day, and exceeding that can cause nausea and interfere with copper absorption. Zinc is not a proven preventive measure, and taking it daily to ward off illness isn’t recommended.
The Basics That Add Up
Beyond the big-ticket items, a few smaller habits reduce your exposure throughout the day. Avoid touching your face, particularly your eyes, nose, and mouth, since that’s how most respiratory viruses enter your body after landing on your hands. Keep shared surfaces in your home clean during illness season, especially if someone in your household is already sick. Stay home when you’re ill: this protects others and gives your body the rest it needs to recover faster.
Eating a diet rich in fruits, vegetables, and whole grains provides the micronutrients your immune system depends on without requiring supplements. Staying well-hydrated keeps your mucous membranes moist and functional. Managing stress matters too, since chronic stress suppresses immune function through many of the same inflammatory pathways that sleep deprivation does. None of these habits alone is a magic shield, but layered together, they meaningfully reduce how often you get sick and how severe it is when you do.