Researchers at Stanford University in California have identified the mechanisms in the skin that produce feelings of “tightness” after the use of cleansers and alleviate those feelings after moisturization. From these findings, they have developed a model that accurately predicts how patients will experience skin products.
Their work, published in PNAS Nexus, demonstrates how mechanical changes at the outer surface of the skin translate into sensations and provides a quantitative approach for determining how people will perceive their skin after using a moisturizer or cleanser.
“This work provides a new understanding of how products affect the physical properties of our skin, which includes not just skin health, but also skin sensorial perception. That’s a significant advance,” said senior author Reinhold Dauskardt, PhD, in a press release from the university. “It provides a whole new understanding of how to design those formulations.” Dr. Dauskardt is the Ruth G. and William K. Bowes Professor in Stanford’s Department of Materials Science and Engineering.
The researchers note that harsh cleansers strip away some of the lipids that hold moisture in the skin, causing the stratum corneum to contract. A good moisturizer increases the water content of the stratum corneum, causing it to swell.
Dr. Dauskardt and his colleagues predicted that the mechanical forces created by this shrinking or swelling propagate through the skin to reach mechanoreceptors—sensory receptors that turn mechanical force into neurological signals—below the epidermis. These receptors then send signals to the brain that are interpreted as a feeling of skin tightness.
To test their theory, the researchers studied the effects of nine different moisturizing formulas and six different cleansers on donor skin samples from three locations on the human body—cheek, forehead, and abdomen. They measured changes in the stratum corneum in the lab and then fed that information into a sophisticated model of human skin to predict the signals that the mechanoreceptors would send.
“We were able to rank the different formulations in terms of what subjects should say about the sensorial perception of their skin,” Dr. Dauskardt said.
The predictions from their analysis lined up almost perfectly with what people reported in human trials for each formula. Collaborators at L’Oréal Research and Innovation recruited 2,000 women in France to assess the nine moisturizers and 700 women in China to assess the six cleansers. The participants ranked their perceived feelings of skin tightness after using the formula they were given.
“We plotted what we were predicting against what human subjects were telling us, and it all fell on a straight line. In other words, we were predicting exactly what they were telling us,” Dr. Dauskardt said. “It was an absolutely remarkable correlation with a very high statistical significance.”
In the release, the authors note the ability to understand and predict how people will feel after using a skin treatment could help cosmetics companies improve their formulations before bringing in people to test them. And with such a detailed model of how mechanical stresses are transferred through skin layers, these methods could potentially be used to evaluate more than just the feeling of tightness, Dauskardt said. “It provides a framework for the development of new products,” Dr. Dauskardt said. “If you’re doing anything to the outer layer of the skin that’s causing it to change its strain state and its stress state, then we can tell you how that information is transmitted and how it will be understood and reported by consumers.”
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