One of the primary challenges in preventing dry skin conditions is the lack of direct physical sensations indicating that humidity and temperature stresses are impacting skin. Except at elevated humidities in which moisture on skin produces discomfort, humidity is not a strong determinant of indoor thermal comfort. In fact, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) does not even specify a lower bound level of humidity in its standard entitled “Thermal Environmental Conditions for Human Occupancy” (i.e., ASHRAE Standard 55).
The lack of physiological indicators of skin drying stressors along with the low sensitivity of thermal comfort to humidity means that people have no way of knowing when to use skin moisturizers or room humidifiers to prevent dry skin! Instead, millions of people simply deal with dry skin after it appears, and then delayed treatment with over-the-counter moisturizers may take longer to become effective.
One proactive solution is to monitor the Dry Skin Index (DSI) that is determined from measurements of both indoor relative humidity and temperature. As skin drying stresses increase due to changes in seasonal weather patterns—for example, when cold, dry outdoor air enters a heated house—skin-care practices can be tailored to respond accordingly. Even individuals who use moisturizers on a daily basis would benefit from monitoring the DSI because they could adjust the amount or frequency of moisturizer applications based on monitoring results.