Research Links Facial Cleanser to Skin Tightness

When we use a cleanser on our faces, our skin can get tight. That discomfort is often relieved by using facial cleanser. This experience of our skin may appear subjective, but Stanford researchers have revealed the mechanism underlying these feelings.

Their research, which was published this week in PNAS Nexus, reveals how mechanical changes at the skin’s outer surface translate into sensations and provides a quantitative approach for predicting how people would perceive their skin after using a facial 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 Reinhold Dauskardt, the Ruth G. and William K. Bowes Professor in Stanford’s Department of Materials Science and Engineering. “It provides a whole new understanding of how to design those formulations.”

Sensation forecasting

Our skin is the greatest organ in our bodies, and it is continuously exposed to the environment around us. The stratum corneum, or outermost layer of our skin, functions as a barrier to keep out harmful chemicals and bacteria while also keeping moisture in. When we use a harsh cleaner, it removes some of the lipids that hold moisture in, causing the stratum corneum to constrict. A excellent moisturizer increases the water content of the stratum corneum, causing it to swell.

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 convert mechanical force into neurological signals – beneath the epidermis, which then send signals to the brain that we interpret as a feeling of skin tightness.

To put their idea to the test, the researchers examined the effects of nine different moisturizing formulae and six different cleansers on donor skin samples taken from three different sites on the human body: the cheek, forehead, and abdomen. They examined changes in the stratum corneum in the lab and then plugged that data into a sophisticated model of human skin to forecast the signals that the mechanoreceptors would convey.

“We were able to rank the different formulations in terms of what subjects should say about the sensorial perception of their skin,” Dauskardt said.

Their analysis’ predictions matched almost exactly what participants reported in human trials for each formula. L’Oréal Research and Innovation collaborators recruited 2,000 women in France to test the nine moisturizers and 700 women in China to test the six cleansers. The subjects rated their subjective experiences of skin tightness after using the solution.

“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,” Dauskardt said. “It was an absolutely remarkable correlation with a very high statistical significance.”

Influencing new developments
Understanding and predicting how people would feel after taking a skin treatment could help cosmetics businesses improve their formulas before putting them through human testing. With such a thorough description of how mechanical stresses are distributed via skin layers, Dauskardt believes these approaches might be used to assess more than simply the sensation of tightness.

“It provides a framework for the development of new products,” 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.”

Dauskardt hopes to use his new knowledge to the creation of wearable technologies. For instance, if we understand how our brains read minute variations in skin tension, we may be able to use that mechanism to send purposeful signals. A device that creates minute mechanical changes on our skin may be able to transfer information in the same way that a person reading braille converts sensations on their fingertip into words.

“What we’ve done is reveal how mechanical information gets from the outer stratum corneum layer down to the neurons much lower in the skin layers,” Dauskardt said. “So now, can we communicate through human skin? Can we build a device to provide information to someone non-verbally, non-visually, using our understanding of these mechanisms? That’s one of the areas we’re very interested in.”

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