The Simple Flu Fix Hiding In Your Thermostat

When flu season ramps up, most of us think about hand sanitizer, vitamin C and whether we remembered to get a flu shot. But there’s another line of defense quietly working (or not working) inside your home: humidity.

According to meteorologist Rob Shackelford, indoor humidity plays a surprisingly big role in how easily viruses spread and how your body handles them once they’re in the air. The goal? What he calls the “40-60 indoor humidity rule.”

“This is just your sweet spot of humidity you want in your entire house. Everywhere, every room, no dead spots," Shackelford explained.

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He’s talking about relative humidity, which is the percentage of moisture in the air compared to how much the air can actually hold. One hundred percent relative humidity usually means rain (not something you want happening in your living room), but air that’s too dry isn’t doing you any favors either.

(MORE: How Weather Impacts Flu Outbreaks)

In air below about 40% relative humidity, viruses can stay airborne longer, making it easier for you to touch or inhale them. But if you keep your air in Shackelford's relative humidity "sweet spot," the humidity can help pull those viruses out of the air.

“The phrase I love to say is weighted down,” he explained. “It weighs down viruses that are airborne and makes them a little bit harder to get to you.”

Dry air doesn’t just help viruses spread. It can also irritate your body directly.

“When you have relative humidities in your house below 40, it just feels like you’re in a desert,” Shackelford said. “You feel that dryness in your mouth and throat, and that is where illnesses can come in.”

That dryness can lead to scratchy throats, dry coughs and irritated airways, especially for people with asthma or other respiratory conditions, which is why monitoring your home's humidity is “really imperative” for sensitive lungs.

(MORE: The Truth About Cold Weather Wives Tales)

On the flip side, too much humidity creates a whole different problem. Above 60%, things can turn muggy fast, allowing mold and mildew to move in.

“If you’re exposed to mold and mildew for that long, don’t be surprised if you have upper respiratory issues,” Shackelford warned. “It’s really not good.”

Shackelford recommends keeping tabs on humidity throughout your home, not just in one room. “Even one leak, even one area where there's a pocket of relative humidity that's too high, can impact the rest of your house," he said.

Humidifiers and dehumidifiers can help, especially models that automatically stay within a set range.

(MORE: Our Picks For Best Humidifiers)

You can’t control every virus that comes your way, but you can control the air inside your home. Keeping indoor humidity between 40% and 60% won’t magically make you flu-proof, but it can make it harder for viruses to hang around and easier for your body to breathe comfortably.

When it comes to fighting off illness this flu season, that balance can make a real difference.