Monitor Indoor Drying Stresses on Skin
The Dry Skin Index (or DSI) is used to represent the magnitude of external drying stresses on the outer layer of the stratum corneum. It is calculated from measurements of indoor relative humidity and temperature using a humidity/temperature sensor.
The DSI is a scale from 0 to 10, broken down into the following categories:
Very low (DSI 0 to 2)
Low (DSI 2 to 4)
Moderate (DSI 4 to 6)
High (DSI 6 to 8)
Very high (DSI 8 to 10+)
At low DSI values, humidity is high and the skin is hydrated. The target DSI level is 4, corresponding to an indoor relative humidity of 60% and a temperature of 68 degrees F (20 degrees C). As the DSI increases above 4, drying stresses are rising and the potential need for skin care interventions become more important.
The actual response of your skin to external drying stresses depends on its physicochemical properties such as natural moisturizing agents, which help hydrate skin, and your normal skin-care practices.
The Dry Skin Index changes seasonally in response to local climatic conditions.
The Dry Skin Index derived from indoor temperature and humidity measurements will change in response to seasonal variations in outdoor water vapor levels. To illustrate, the adjacent plot shows average monthly DSI values for a sample of houses in the northeastern US.
In the summer months, the DSI levels are low because high water vapor levels in outdoor air also keep relative humidities indoors high, which reduces drying stresses on skin. Gradually though the fall months, the atmosphere dries out and associated indoor humidities decline, resulting in increases in the DSI.
Monitoring the DSI specific to your house will help you implement the appropriate skin-care options.
UV Exposure Index
The UV index uses a scale from 1 to 11+ to indicate the severity of ultraviolet irradiation, and includes a biologically-weighted integration of both UVA and UVB radiations.
The chart below shows the hourly Clear Sky UV Index predicted for your location (determined from your IP address) using an ozone forecast (ozone adsorbs UV radiation) and elevation (UV radiation increases with elevation). These hourly UV predictions can be considered upper-bound values because they do not incorporate reductions due to cloud cover, rain, etc.