Focusing on previous studies on the effects of low humidity that obtained subjective reports of humans, the findings to date are summarized in this paper. Humans are affected by low humidity and show psychological responses to low humidity, but in most cases, these responses are weak, and even if humidity is very low, many subjects answer “slightly dry” or “not dry.” In other words, it is difficult to see differences in subjective reports between different humidity conditions. Therefore, the degree of involvement of humidity in human health is not yet clear, and the humidity level that should be maintained has not yet been determined from the subjective report data. The response on the “dry” side at low humidity is often weak, but there are a few clear “dryness” being declared. Therefore, by evaluating individual data rather than the average of multiple subjects, by asking about the sensation of each part of the body, and by selecting evaluation words that are closer to the physical sensation, the effects of low humidity may be clarified.

WBGT (wet bulb globe temperature) is used in Japan as an index to alert people in general about the risk of heat stroke, although it was originally developed as a measure of the heat stress for people performing strenuous activities, such as outdoor works and athletic activities. In an effort to raise public awareness of WBGT as a part of heat stroke prevention measures, an illustration that attempted to explain natural wet bulb temperature, which is used to obtain WBGT, as an indicator of humidity has been widely quoted and spread. This illustration has led to the misconception that humidity accounts for 70% of the WBGT while air temperature accounts for only 10%. Needless to say, it is extremely dangerous to focus only on humidity and disregard temperature in formulating heat stroke countermeasures, and if inappropriate actions are taken based on the misconception, the risk of heat stroke may actually increase. Therefore, it is vital to clarify the widespread incorrect explanation of WBGT and to provide the public with correct knowledge on how temperature and humidity together affect the body’s ability to release heat and cause heat stroke.