Why You Get Sick in Cold Weather
It’s a tale as old as time. You’ve probably heard of the common myth that cold weather makes you sick.
When temperatures drop, you tend to huddle inside. You bundle up. And just when you think you’re taking all the necessary precautions, here you go again–reaching for another box of tissue, cuddling up on the couch, with a cold. Should you just stay inside all winter long?
The question isn’t whether you get sick more when it’s cold outside. We all do—the data is clear on that. The question is why. Understanding the different mechanisms at play will completely change your self-care in the winter.
The air quality problem
We spend about 90% of our time indoors regardless of the weather. So if the cold air isn’t making us sick, then what is? Part of the problem is a result of our indoor air quality when temperatures drop.
According to epidemiology, seasonal illness patterns are largely driven by indoor climate conditions and air circulation in our homes. Both are influenced by outdoor conditions.
With central heating and increasingly airtight buildings, we create an indoor climate dramatically different from outdoors. Heating dry, cold air causes the relative humidity to drop significantly. Relative humidity refers to the amount of water vapor in the air compared to how much there could be.
Measurements from New York apartments and Midwest commercial buildings showed indoor RH below 24% in the winter—far below the optimal range at 40-60%. This facilitates the spread of viral infections.
But why does dry air matter for getting sick?
It turns out your body’s defenses depend heavily on moisture. Low humidity weakens your nose’s natural defenses.
Your nasal passages are lined with cilia—tiny, hairlike structures that trap viral particles and moisturize the air you breathe. When indoor humidity drops below 40%, this natural defense system breaks down.
Cilia movement slows down significantly, reducing your body’s ability to clear pathogens. In addition, the protective mucous lining of your airways becomes impaired, which allows viruses to enter your body more easily.
Remember, viruses actually love winter weather!
Influenza viruses can remain stable and infectious at low humidity levels (20-50%) combined with comfortable indoor temperatures (68-72°F).
When you cough or sneeze, the droplets released shrink in the cold air, becoming tiny viral particles that remain in the air for hours. Even worse, low humidity preserves the virus’s outer coating, enabling it to survive longer indoors.
This creates a dangerous combination: viruses are surviving longer in the air, and your body is less equipped to fight them off.
Now that you know what’s really happening, what can you do?
- Optimize indoor humidity levels
Studies consistently show that maintaining indoor humidity between 40-60% significantly reduces viral transmission. At this level, viruses become less stable and droplets behave differently, reducing your risk of infection.
The most effective way to do so is with a humidifier. It adds moisture to the air and helps maintain the relative humidity level indoors.
- Improve indoor ventilation
Open your windows or backyard door for 5-10 minutes a few times daily to refresh indoor air—yes, even in the winter. Most modern homes are so airtight that intentional ventilation matters a great deal.
- Support your body’s built-in defenses
Use a saline rinse or neti pot daily during the cold season to moisten your nasal passages and keep them clear. You can try steam inhalation for quick relief, and stay hydrated to keep your airways functioning properly.
To be clear: you absolutely need to heat your home in the winter. The issue isn’t the warmth itself—it’s that heating creates dry air as a side effect, which needs to be addressed. Now that you better understand the actual mechanisms at play, you can take control of your indoor environment and stay healthier all winter.
