The most effective way to prevent colds and flu is layering several simple habits: washing your hands properly, getting enough sleep, staying physically active, and getting a yearly flu vaccine. No single strategy eliminates your risk entirely, but combining them creates meaningful protection. Here’s what the evidence says about each one and how to get the most benefit.
Wash Your Hands for 20 Seconds
Proper handwashing reduces your risk of respiratory infections like colds by about 20%. The key word is “proper.” Scrubbing for at least 20 seconds removes significantly more germs than shorter washes. That’s roughly the time it takes to hum “Happy Birthday” twice. Lather the backs of your hands, between your fingers, and under your nails, then rinse and dry thoroughly.
The times that matter most are before eating, after using the bathroom, after blowing your nose, and after touching shared surfaces like doorknobs, elevator buttons, or shopping carts. When soap and water aren’t available, an alcohol-based hand sanitizer with at least 60% alcohol is a reasonable backup, though it’s less effective on visibly dirty hands.
Sleep Gives Your Immune System a Direct Boost
Sleep doesn’t just help you feel rested. It triggers a specific immune process: during sleep, your body releases growth hormone and prolactin, two hormones that help T-cells (a critical type of immune cell) migrate to your lymph nodes. That migration is essential for your body to recognize and mount a defense against new infections. When you stay awake through the night, this process is measurably impaired.
Most adults need seven to nine hours per night. Consistently sleeping less than that leaves your immune system less prepared to fight off the viruses you encounter daily. If you’re someone who catches every cold that goes around your office or household, poor sleep is one of the first things worth examining.
Exercise Cuts Sick Days Nearly in Half
People who do moderate aerobic exercise five or more days a week, in sessions of at least 20 minutes, experience 43% fewer days with upper respiratory symptoms compared to people who exercise once a week or less. That’s a striking difference for something as simple as a brisk walk, a bike ride, or a swim.
The benefit comes from moderate, consistent activity. Occasional intense workouts don’t offer the same protection, and extremely prolonged or grueling exercise can temporarily suppress immune function. The sweet spot is regular movement that raises your heart rate without leaving you exhausted.
Get a Flu Vaccine Every Year
There’s no vaccine for the common cold, but the seasonal flu vaccine remains one of the most direct ways to protect yourself against influenza. Effectiveness varies from year to year depending on how well the vaccine matches circulating strains. For the 2024-2025 season, the CDC’s interim estimates put vaccine effectiveness for adults at 36% to 54% against outpatient flu illness and 41% to 55% against flu-related hospitalization. For children and adolescents, effectiveness ranged from 32% to 60% in outpatient settings and 63% to 78% against hospitalization.
Those numbers might seem modest, but even partial protection reduces the severity and duration of illness if you do get infected. The vaccine is reformulated each year, so last year’s shot won’t cover this year’s dominant strains.
Keep Indoor Humidity Between 40% and 50%
Dry indoor air, common during winter when heating systems run constantly, helps influenza viruses survive longer and spread more easily. Research modeling viral transmission found that raising indoor relative humidity from 20-30% to around 50% meaningfully decreases the infection risk for influenza. Below 40%, the virus remains infectious in the air for longer periods, and your nasal passages dry out, reducing their ability to trap and clear pathogens.
A simple hygrometer (available for a few dollars at most hardware stores) lets you monitor humidity levels at home or in your office. If readings consistently fall below 40%, a room humidifier can help. Aim for 40-50%, as going above 60% creates conditions that encourage mold growth.
Vitamin D Supplements May Help
Multiple large analyses have found that vitamin D supplementation lowers the odds of getting a respiratory tract infection. One review of 25 randomized trials covering nearly 11,000 people found a 12% reduction in the risk of experiencing at least one acute respiratory infection. Smaller reviews have reported larger effects, with reductions in the range of 36% to 42%.
The benefit appears strongest in people who are deficient in vitamin D to begin with, which is common during winter months, in people with darker skin, and in those who spend most of their time indoors. If you suspect your levels are low, a blood test can confirm it. Many adults in northern latitudes fall below optimal levels between October and March.
Zinc Lozenges Shorten Colds Once They Start
Zinc won’t prevent you from catching a cold, but it can significantly reduce how long one lasts if you start taking it early. A meta-analysis of three randomized trials found that zinc acetate lozenges providing 80 to 92 milligrams of zinc per day shortened the total duration of colds by 42%. The catch is timing: the lozenges need to be started within the first 24 hours of symptoms to be effective.
Zinc lozenges can cause nausea and leave a metallic taste, so they’re not pleasant. But for people who want to recover faster when they do get sick, keeping a supply on hand is a reasonable strategy.
Probiotics Show Promise but Vary by Strain
Certain probiotic strains appear to lower the incidence of upper respiratory infections, though the evidence is uneven. Not every strain works, and not every study shows a statistically significant benefit. One strain used in fermented dairy products showed a significantly lower risk of catching the common cold compared to placebo, with roughly 60% lower odds in one trial.
If you want to try probiotics for immune support, look for products that specify the strain on the label, not just the species. The strains with the most evidence behind them for respiratory protection tend to be from the Lactobacillus family and are commonly found in fermented dairy products like yogurt and kefir. A generic “probiotic blend” may or may not contain strains that help with respiratory immunity.
Saline Nasal Spray as a Daily Habit
Rinsing your nasal passages with saline isn’t just for allergy sufferers. In a study of healthy adults, using a daily saline nasal spray reduced the number of days spent with nasal congestion or runny nose from an average of 11 days to about 6 days over the study period. Participants also averaged fewer episodes of upper respiratory infections: 0.7 during the spray period versus 1.0 during the observation period.
Saline sprays are inexpensive, available without a prescription, and have essentially no side effects. They work by keeping the nasal lining moist and helping clear out viral particles before they can establish an infection. Using one after commuting on public transit or spending time in crowded spaces is a low-effort habit with real payoff.
Putting It All Together
No single habit makes you bulletproof against colds and flu. The power is in stacking multiple layers of protection. Wash your hands thoroughly throughout the day. Sleep seven to nine hours. Move your body most days of the week. Get your annual flu shot. Keep your indoor air from getting too dry. Consider vitamin D if your levels are low, and keep saline spray and zinc lozenges within reach. Each of these strategies chips away at your overall risk, and together they add up to noticeably fewer sick days each year.