New York, Sep 27 : Ever wondered why the skin on your face feels tight after washing with a cleanser? Research shows it is due to contraction of the stratum corneum, the outermost layer of our skin. Skin is the largest organ in the body and it's constantly exposed to the environment around us. The stratum corneum acts as a barrier to keep out unwanted chemicals and bacteria and to keep up the moisture. Researchers at Stanford University in the US show how mechanical changes in the outer surface of our skin translates into sensations and provides a quantitative approach for determining how people will perceive their skin after using a moisturiser 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 Reinhold Dauskardt, Professor in Stanford's Department of Materials Science and Engineering. The team predicted that the mechanical forces created by this shrinking or swelling propagates through the skin to reach mechanoreceptors (a sense organ) below the epidermis, which then fire off signals to the brain that we interpret as a feeling of skin tightness. In the study, published in 'PNAS Nexus' journal, researchers studied the effects of nine different moisturising 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. 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 moisturisers 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. '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,' said Dauskardt. '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 noted. /IANS