Does everyone in your house get sick once you turn on the heat?

You turn on the heating for the first time in autumn and you feel like everyone is suddenly getting sick. It’s not a figment of your imagination – and it’s not just the weather that changes.

This is the effect of heating on indoor humidity.

When cold air from outside warms indoors, relative humidity can drop by up to 20%, depending on researchers who say desert air prepares you for illness.

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(MORE: If You’re Having a Mental Crisis, It May Be Due to Your Allergies)

What’s happening to you

Dry indoor air thins and dries out the critical mucus lining your nose and throat; it’s your first defense against incoming viruses. This lining and microscopic structures called cilia usually trap and remove viral particles.

A Yale study even found that mice breathing dry air were more susceptible to influenza than mice breathing humid air.

What happens to a virus

In dry air, virus-carrying droplets become smaller, stay airborne longer, and travel farther, giving them a greater chance of infecting you.

A study Using SARS-CoV-2 as a test case, it was found that dry indoor conditions typical of winter kill viruses more slowly than wetter summer conditions, thereby increasing the concentration of virus particles in poorly ventilated spaces.

(MORE: Flu season follows humidity, not the calendar)

And then there’s the cold air

The cold air itself also blunts your nose’s defenses, thereby hitting that crucial lining of your nose and throat. Research published in the Journal of Allergy and Clinical Immunology discovered that exposure to cold air directly alters the mucous membranes involved in fighting viruses.

Then there’s the fact that with the heat, many of us will spend most of our time indoors, with windows closed, in close proximity to others, increasing our exposure to potential illnesses.

(MORE: Could you be allergic to the cold?)

So what is the solution?

Improving these indoor conditions is quite simple and cost-effective. Scientists believe that keeping the relative humidity in your home between 40 and 60 percent is the best way to stay healthier.

Most SMART thermostats include a hygrometer that can tell you where you are, or you can buy a digital one for around $20.

If the humidity in your home is below 40%, a humidifier can increase the humidity. Just make sure you clean it properly and regularly to avoid putting more germs into the air!

One more thing: While burping or airing out your home is something we encourage to bring fresh air into your home during the colder months, when you open a window you may want to run the humidifier so you don’t let that indoor humidity fall out.