What relative humdity level is best for building occupants?

Q:What relative humidity (RH) level is best for building occupants?

A: The short simple answer is between 40% and 60% RH (see graph below). At a level below about 32% people start experiencing discomfort in the form of dry eyes, nose, ears and throat. This is very irritating and can lead to health problems such as nosebleeds, sore throats, sinus problems etc. Viruses also start becoming more prevalent at humidities below 30%. Above 60% RH the building runs the risk of microbiological growth (e.g., mold and mildew). Both RH extremes are a direct risk to health and the classic sick building syndrome. Luckily the best RH for health is also the best for comfort. A 50% set point would be the best target with a ±10% swing for summer/winter variations.