Absolutely true! Just because we can't see it doesn't mean it doesn't affect us. Recently the change of seasons and no longer needing to run the furnace I switched off the heat not realizing it also turned off the fan which I run all the time to circulate the air in my home. For weeks I was sneezing and dealing with a constant runny nose. I didn't realize the air circulation had been turned off. I have a UVGI light in my return air duct and I was no longer feeling those benefits without the circulation of air. Once I realized the fan wasn't running it all made sense. Turned the fan back on and within hours the sneezing and constant runny nose ended!