The temperatures dropped just enough this past week that I had to adjust our thermostats, which means the heat will start running at night.



Running the heat leads to drier air in our home, and drier air can lead to an increased risk of colds and the flu.



That got me wondering a few things: What humidity level is best for your health? Is it possible to increase your home’s humidity with an essential oil diffuser? And if the diffuser helps, could the oils help too?



Since I started reading research papers to satisfy my own curiosity, I figured I’d share what I found in case these questions made you curious, too.



How does humidity affect your risk of getting a cold or the flu?



No doubt, you’ve been told to “Put a hat on so you don’t catch a cold” when going outside in colder temperatures.



However, you getting or not getting sick might have nothing to do with the temperature and everything to do with the humidity. 



Cold winter air is dry. So is heated indoor air.



As scientists have known for decades,




influenza infection rates are highest in environments with relative humidity below 40% and decrease rapidly as the relative humidity exceeds 40-50%.
Indirect Health Effects of Relative Humidity in Indoor Environments



For example, school classrooms in northern climates during colder months are often dry. Heating systems dry the air and can increase the risk of kids getting infections.



A Minnesota study found the following:




This study monitored presence, genomic copy number, and infectivity of influenza A virus in preschool classrooms during the dry winter months (low indoor humidity), which correspond with peak respiratory virus infections in Minnesota. An increase in average AH from 6.33 mb in control rooms to 9.89 mb in humidified rooms (RH ~42–45%) was associated with a significant decrease in influenza A virus presence in fomite and air samples in humidified rooms compared to control rooms.
Humidity as a non-pharmaceutical intervention for influenza A



Higher humidity reduced the concentrations of influenza A in classroom air.



Interestingly, the authors of a recent paper published in Biophysical Journal explained that a face mask's benefit, if there is one, could be more to do with its impact on humidifying the air of the wearer than it has to do with keeping viral particles out of their nose or mouth.




The increased humidity of inspired air associated with wearing a face cover is perhaps well recognized by the public and contributes to the general feeling of mugginess, in particular when the weather is humid. Our measurements confirm that the increased humidity of inspired air is real and quite large.




They go on to say:




We propose that the increased humidity of air inspired through face masks is responsible for the lower disease severity of mask wearers.
Hydrating the respiratory tract: An alternative explanation why masks lower severity of COVID-19



If that’s the case, a ski mask or gator in winter weather could help as well, as they also humidify the air you breathe. Keep in mind that if your mask is too damp for too long, it’ll become a breeding ground for mold and some bacteria.



It’s probably better to save the mask-wearing for the cold outdoors, and find a different way to increase the humidity indoors. 



Though we run multiple diffusers every day, which adds some humidity to our home's air, I've never paid attention to exactly what the relative humidity is in our home. After reading about it to prepare for this blog post, I plan to purchase a hygrometer this fall and make sure our home stays humid enough.



On another note, higher vitamin D levels are also associated with lower rates of seasonal illness. I covered that in this article: Vitamin D: Deficiency Symptoms And Benefits Of Supplementation.



Isn't high humidity bad, too?



You’ve no doubt seen the effect of high humidity in your bathroom. It grows mold.