Track the Dry Skin Index for Better Skin Care during the Winter

If you experience dry, flaky skin—especially during the colder months of the year—then it will probably be beneficial for you to monitor changes in the Dry Skin Index (DSI). As I explain in another blog entry, this proprietary index measures the external drying stresses on skin caused by indoor humidity and temperature. Both of these parameters of indoor air change on a seasonal basis as a function of the levels of water vapor in outdoor air, building properties, severity of the heating season, etc.

Responding to Seasonal Changes in the Dry Skin Index

The chart below shows the monthly average DSI values calculated for a sample of houses in the northeastern US (based on data from Arena et al., 2010). The drying stresses on skin increase by almost a factor of 2 from the low value in July to the high in January. These seasonal changes in the DSI values directly coincide with the frequency of Internet searches for information regarding “dry skin” as well as “winter dry skin”. Unfortunately, because you really can’t sense the magnitude of these drying stresses on skin, it’s difficult to adapt skin-care practices in a timely manner to compensate for the external stressors. Consequently, skin-care practices are often “after-the-fact”, that is, you only consider the use of a moisturizing lotion or cream until after flaky, dry or itchy skin develops.

Average monthly values of the Dry Skin Index for a sample of houses in the northeastern US.

Average monthly values of the Dry Skin Index for a sample of houses in the northeastern US.

October marks the transition from the warm, humid summer months to the start of the heating season accompanied by cooler, drier outdoor air. If you are susceptible to dry skin during the fall and winter months, this is a good time to stock up on moisturizing lotions and creams when sales occur at your favorite skin-care shopping place.

Adjusting Dry Skin Care for Winter Cold Spells

The occurrence of “cold spells” during the winter will produce elevated drying stresses on skin. For example, the cold, dry air associated with an arctic air mass will drive indoor humidities lower, resulting in DSI levels that are higher than the monthly average values depicted in the chart above. If you’re not able to monitor the increased drying stresses on your skin that occur during such cold spells, you won’t be able to adjust your skin-care practices in a timely manner to maintain proper hydration of the stratum corneum—or the outer most layer of skin.

Buildings, Climate, and the Dry Skin Index

Residential populations living in buildings that do not easily retain moisture and/or have high air exchange rates with outdoor air will be exposed to elevated drying stresses on skin and thus have an increased risk of having cosmetic (i.e., flaky) dry skin conditions. The next chart depicts the DSI levels calculated for a sample of apartments in New York City (NYC) monitored by Quinn and Shaman (2017). Note that the levels are considerably higher than the values associated with the detached residences shown in the prior chart even though the residences are in essentially the same climatic zone! The average wintertime DSI for the detached residences is 6.6, compared with 8.1 for the NYC apartments.

Monthly average values of the Dry Skin Index for a sample of apartment buildings in New York City.

At such elevated drying stresses, the likelihood of flaky dry skin increases dramatically. In this situation, the use of a room humidifier becomes an important tool for reducing the DSI by increasing indoor humidity. Nevertheless, Quinn and Shaman (2017) found that ownership of a humidifier among the apartment residents was not associated with a significant increase in humidity. Perhaps if those residents had been able to monitor the drying stresses in their apartments, humidifier use would have increased to improve skin hydration.

Wrap Up

  • Millions of people live in cold climates where wintertime dry skin is a challenge to deal with.
  • Drying stresses on skin in indoor environments can vary considerably—even in the same climatic zone.
  • Monitoring drying stresses on skin can inform skin-care decisions ranging from the application of over-the-counter moisturizing lotions to the operation of humidifiers for nighttime hydration of skin.


Arena, Lois and Mantha, Pallavi and Karagiozis, Achilles N., Monitoring of Internal Moisture Loads in Residential Buildings (December 1, 2010). Available at SSRN:

Quinn, Ashlinn, and Jeffrey Shaman. 2017. “Indoor Temperature and Humidity in New York City Apartments during Winter.” Science of The Total Environment 583: 29–35.