DSI and Skin Hydration in Tuscon, Arizona
I recently calculated values of the Dry Skin Index (DSI) and the water content of skin from 365 days of relative humidity and temperature measurements taken in my residence in Tucson, Arizona. As shown in the adjacent chart, the DSI and skin hydration levels follow distinct seasonal patterns. These patterns are controlled primarily by water vapor levels in outdoor air and the building properties of my residence (e.g., air exchange rates, water absorption/desorption from building materials, and indoor temperatures).
The most striking feature of the chart is the 7-month period from November to June when dry-skin stressors are the greatest. During this timeframe the DSI exceeds a value of 5 (indicative of moderate drying stresses) and the estimated water content of the outer layer of the stratum corneum (expressed in grams of water per mL of skin) drops well below a target level of 0.10 g/mL, which corresponds to a relative humidity level of 60% in ambient air (see the blog "The Target Hydration Level for Skin"). The highest levels of ambient water vapor occur during Tucson’s summer monsoon season, which begins in June or July when atmospheric conditions promote the transport of moisture from Mexico that subsequently increase humidity levels and trigger thunderstorms in southeast Arizona. Consequently both the DSI and skin hydration levels change rapidly, reducing skin drying stresses—but only until the monsoons end in September and drying trends begin again (as shown in the plots).
By monitoring the seasonal changes in skin stressors, I’m better able to prevent the occurrence of dry skin by proactively applying moisturizing lotions/creams and by operating a bedroom humidifier when indoor humidities are low. Historically though, my dry skin care was only initiated in response to dry skin—mainly because I was unaware of the impact of drying stresses on my skin. In fact, one of the surprises for me in studying the DSI plot was the long duration of the environmental stresses, which means that my personal skin care requires an ongoing commitment to moisturizer applications that correspond to the magnitude of external skin stressors.
- The unique, dry desert climate of Tucson, Arizona, produces a distinct seasonal variation in drying stressors on skin.
- By monitoring those stressors, dry skin care can be adjusted to compensate for those stressors, helping to prevent undesirable conditions such as itchy dry skin and dandruff.
- Although the focus of this Skin Care Blog is on Tucson, the climate of where you live as well as the building properties of your residence will produce a different set of seasonal dry skin stresses—and thus the need to monitor and adapt your personal skin care as appropriate.