Background: A pressure ulcer is localized tissue injury to the superficial layer of the skin and/ or the underlying tissue. Pressure ulcers are most likely to develop in skin areas exposed to pressure, shear and friction. Shear- force is an important contributing factor and wound dressing are possibly capable to reduce shear force at the skin. At this moment there's no good marker to detect the effect of shear- force at the skin. A potential marker could be cytokines (IL-1α) which are released after mechanical loading of the skin. A previous study have shown a significant increased level of IL-1α after the application of pressure. We want to investigate if these cytokines are significant increased after the application of shear- force at the skin.