REVIEW ARTICLE Environmental dew point and skin and lip weathering C Devillers, † GE Pie ´ rard, †, * P Quatresooz, † S Pie ´ rard, ‡ † Laboratory of Skin Bioengineering and Imaging, Department of Dermatopathology, University Hospital of Lie ` ge, Lie ` ge, Belgium ‡ Department of Imaging and Telecommunication, University of Lie ` ge, Lie ` ge, Belgium *Correspondence: GE Pie ´ rard. E-mail: Gerald.pierard@ulg.ac.be Abstract Xerosis represents a physiological response of the stratum corneum (SC) to environmental threats. The influence of the environmental dew point (DP) is not fully understood. This parameter is the air temperature at which the relative humidity is maximum. This study aimed to assess the relationship between the environmental DP and the water- holding capacity of the skin and lower lip vermilion. For comparison, SC property was evaluated after occlusive application of cooled and uncooled hydrogel pads. Electrometric measurements using a dermal phase meter (DPM) device were performed on the back of the hands, the cheeks and the lower lip of 40 healthy menopausal women. Assessments were performed in the outdoor conditions during winter and spring. The same measurements were recorded after hydrogel pads, at room temperature or cooled to 4 °C, were placed for 15 min on the test sites. The environmental DP was recorded at each evaluation time. The SC water-holding capacity was discretely influenced by the DP. In the open-air environmental conditions, a positive linear relationship was found on the cheeks between the DP and DPM values. The relationship was weaker on the lips. Conversely, a consistent increase in DPM values was recorded immediately after removal of the cooled and uncooled hydrogel pads. The observations made in the open-air testing conditions are consistent with the predicted events following the Arrhenius law. By contrast, the combination of cooling and occlusion by the hydrogel pads is responsible for the reverse effect on the SC. Received: 26 May 2009; Accepted: 16 September 2009 Keywords cooling device, electrometric property, environment, ice-like water, Stratum corneum, xerosis Conflicts of interest None declared. Introduction With the sustained progression in molecular biology and advanced biophysical techniques, the recognized function of the stratum corneum (SC) does not anymore appear to be restricted to an inert physicochemical protective barrier alone. Rather, the SC structure changes in time resulting from interactions and respon- siveness to its environment. In these respects, the skin adapts to some extent to a cooler environment than the 37 °C of internal organs. However, the physiological adaptation to cold without damages remains limited. The effect of low temperature on the global skin biology is further modulated by the combination of environmental moisture, wind speed and altitude. 1 There is clinical evidence that long-standing environmental changes influence skin biology and alter the structure and functions of the SC. Winter xerosis is the archetype of such changes. 2–7 Such clinical evidence clearly shows that the epidermis is not simply an inert membrane following the rules of physics, but rather it responds to environmental stress by modifying its structure, properties and perhaps reactivity to the sustained envi- ronmental stress. This concept is widely accepted by scientists. As a consequence, it is recommended for most skin bioinstrumental assessments to record and control, when possible, the environ- mental temperature and relative humidity (RH). Relative humidity is defined as the ratio between the amount of water vapour in the air and the amount necessary for saturation at a given temperature. For a given RH, air moisture decreases with temperature. Hence, a relevant representation of the amount of air moisture is given by the dew point. 2 This parameter is defined as the air temperature at which the gaseous moisture begins to condense, i.e. when RH reaches 100%. 8–10 Early clinical studies suggested a relationship between skin dryness and critical drops in dew point. 8 In addition, electrometric properties of the SC were found to be influenced by seasonal variations in both the environ- mental dew point and the perception of sensitive skin. 9 In addi- tion, it is noteworthy that the values of transepidermal water loss (TEWL) are influenced by the temperature at the interface ª 2009 The Authors JEADV 2010, 24, 513–517 Journal compilation ª 2009 European Academy of Dermatology and Venereology DOI: 10.1111/j.1468-3083.2009.03465.x JEADV