What levels of the Dry Skin Index initiate dry-skin formation?

A fundamental issue impacting our personal skin care is the inability to sense the magnitude of drying stresses on skin. This really inhibits the timely and effective use of skin moisturizers and/or humidifier. But what levels of the Dry Skin Index might trigger dry-skin formation?

The Dry Skin Index is broken down into five stress categories ranging from very low to very high. Previously we identified the optimum relative humidity associated hydrated skin, but not the DSI levels at which people should begin to hydrate skin. Fortunately, data derived from a study by Jin et al. (2021) allows us to identity key threshold levels.

DSI levels of 4.4 for seniors and 4.8 for young adults represent thresholds for dry-skin formation

Jin et al. measured the hydration of the stratum corneum on the forearms of 22 subjects. They also recorded the ambient temperatures and absolute humidities in their residences. Absolute humidity is simply the concentration of water vapor in air, expressed in units of g/m³ or g/kg. The subjects were divided into a younger group averaging 24.4 years, and an older group averaging 76.8 years.

The researchers analyzed the relationships between absolute humidity and stratum corneum hydration and showed that the two age cohorts differed in their responses to indoor drying stresses. Specifically, the older cohort became susceptible to dry skin formation at a level of absolute humidity that was lower than for the younger cohort. The equivalent threshold levels expressed as Dry Skin Index levels were 4.4 and 4.8, for the older and younger groups, respectively.

Take home message for your skin care

As people age, their skin gradually becomes less able to respond to indoor drying stresses. So, it is not surprising that the DSI trigger level for dry-skin formation was lower for the older subjects. The trigger DSI levels derived from the Jin et al. study are associated with the low end of the Moderate stress category, that is, DSI levels between 4 and 5. Depending on your age and the properties of your skin, it is prudent to start using moisturizing lotions to keep your skin hydrated when the DSI exceeds 4. Alternatively, start examining areas of your skin that are prone to dryness so that you can initiate moisturizer applications at the first signs of dryness!

However, when the DSI exceeds 5, it is time to begin the regular use of moisturizers on your body and face. Use the free Skin Sim app or the Dermidia Select web app to scope out the periods of the year when your skin is at increased risk of dryness.

Reference

Jin, Yi, Fan Wang, Sarah R. Payne, and Richard B. Weller. “A comparison of the effect of indoor thermal and humidity condition on young and older adults’ comfort and skin condition in winter.” Indoor and Built Environment (2021): 1420326X211030998.