Quantification of the mechanical effects of saline on human ex vivo stratum corneum

The stratum corneum (SC) acts as the body's inert barrier to the outside world, protecting viable tissue from potentially damaging environmental factors. One of the fundamental functions of the SC is to maintain water in the skin by minimizing trans-epidermal water loss (TEWL). When the SC degrades, the ability to hold water in the underlying tissue is reduced, increasing TEWL, exposing the skin to xerosis and potential fracture if left untreated. It is a widely described urban myth that people experience dry and tight ‘weathered’ skin after swimming in the ocean during trips to the beach. It is unknown, however, to what degree saltwater is responsible for the barrier disruption that leads to the feeling of this dry skin. In this initial investigation, we study the impact of saline water treatment on the elastic modulus and drying stress build up within ex vivo SC in comparison with pure water using an established high-throughput mechanical method. Saline was found to cause significantly higher elastic moduli ($E_{SC}=5.13\pm 1.20$ MPa) and drying stresses ($P_{SC}=208.5\pm 24.0$ kPa) in the SC as opposed to deionized water ($E_{SC}=2.75\pm 0.89$ MPa, $P_{SC}=91.23\pm 25.55$ kPa) ($p=0.018,p=0.003$), indicating that exposure to saltwater significantly alters the drying behavior of the SC. This disrupted barrier could lead to xerotic skin. It also appears to explain the anecdotal experience of dry and tight-feeling skin following swimming in the ocean or seawater.