The effect of physical and chemical injuries on transepidermal water loss and turnover time of hairless mouse skin.

Traditional test of skin irritancy or injury involve nonparametric grading scales and rely heavily on an investigator's ability to visually grade the effects of, and recovery from, an injury. Such subjective methods are prone to observer bias. An objective means of assessing wound healing is needed to overcome investigator bias and offset the inherent limitations of nonparametric grading scales. It has been well documented that a non-abrading skin injury causes changes in some objectively measurable properties of the skin. These include the increases in transepidermal water loss and turnover rate seen after skin irritation or injury. The purpose of this research is to develop the basis for a test to assess skin injury that utilizes these two objective measurements. Turnover time and transepidermal water loss determinations were used to assess the effect of several different types of injuries on the skin. Chemical irritation due to surfactant application, as well as physical insults such as sunburns and tape stripping injuries, were shown to increase transepidermal water loss in a dose dependent fashion. Correlations were drawn between the severity of the injury and the subsequent increase in transepidermal water loss. These injuries were also shown to increase the turnover rate (decrease the turnover time) of the tissue. These effects could be ameliorated, prevented or exacerbated with topical applications of sunscreens and steroids. These techniques provided a quantifiable assessment of the degree of protection provided by commercial and experimental sunscreen formulations. Turnover time and transepidermal water loss determinations were also used to assess the effect of the age of an animal on its ability to respond to and recover from an injury. It was shown that the response (turnover) of older animals was slower for uninjured as well as injured skin. This research establishes that turnover time and transepidermal water loss determinations are sensitive and quantifiable indices of various skin injuries.