The determination of an acceptable range of humidity is complicated by the conflicting effects of an increase or decrease in humidity levels on the speed of chemical interactions and growth of biological organisms and pathogens that may affect human health and comfort. Ideally, ventilative characteristics of offices and dwellings should strive for levels of humidity that not only are perceived as comfortable but also minimize the growth of organisms and the speed of chemical processes that will cause discomfort and illness once they are present in sufficient quantity. A review of the relevant health literature suggests that the optimal conditions to minimize risks to human health occur in the narrow range between 40 and 60% relative humidity at normal room temperatures. Although this range is much narrower than the current ASHRAE standard, reducing the range of acceptable humidity would help alleviate many of the health and comfort problems in buildings, especially those that appear to plague modern, sealed office structures.