Sensorial and physiological response in the skin device interaction for personal care/devices

Abstract

Skin sensitivity (SS) is a commonly occurring response to a range of stimuli, including environmental conditions, chemical irritants, and mechanical forces. Factors affecting whether an individual reports SS has been a topic of interest for many years, with studies ranging from questionnaire screening tools to objective measurements of skin characteristics. Despite these studies, there is no consensus regarding a definition of SS. Furthermore, as differences in individual tolerance to stimuli has led to a demand for personalised products, SS continues to be an emerging clinical and social challenge. Consequently, the present research aimed to investigate the variability in skin sensitivity using an array of skin assessment tools. Specifically, mechanical loading in the form of consumer devices were considered, such as electrical shavers where a dynamic combination of pressure and shear is exerted on the skin surface. The bearded area of the cheek and neck in males were selected as regions of interest in context of electrical shaving, enabling examination of inter- and intra-subject variability in perception of enhanced skin sensitivity.
Parameters for characterising skin health were identified following a review of the scientific literature. Findings revealed that the structure and function of the stratum corneum (SC) and its effective barrier properties were closely associated with perception of sensitivity, assessed through parameters such as TEWL, SC thickness, and surface redness. As such, the need for a multifactorial array of skin tissue responses was proposed for understanding the complex pathological mechanisms underlying SS. Furthermore, Optical Coherence Tomography (OCT) was identified as a potential imaging tool to characterise structural and physiological difference in skin sites before and after mechanical stimulation. Consequently, OCT-derived skin parameters were defined and algorithms were developed for estimating values from the cheek and neck. Study I was designed to investigate the short-term effects of several mechanical insults in a consumer panel with a range of self-assessed SS. Study II was designed to investigate the short- and long-term effects of electric shaving where a new stimulus model was developed by introducing repetitive loading, reflecting the real-world scenario where consumers follow a daily shaving routine.
The results presented in this thesis revealed significant spatial differences in the skin tissue, e.g., higher baseline TEWL and temperature was observed on the neck, indicating a weaker skin barrier than the cheek. OCT-derived skin parameters revealed higher basal roughness on the neck. The shaving insult resulted in a decrease in the barrier function accompanied by hyperaemia and inflammation, with the magnitude of the result corresponding to the anatomical site and beard length. Additionally, participants with higher self-reported sensitivity to mechanical stimuli demonstrated higher force values while shaving and higher discomfort post shaving. Remarkably, an increase in the perception of SS and the force of stimulus application correlated with a decrease in the SC integrity, decrease in optical density of the tissue, and a change in the skin reflectivity.
The combination of techniques e.g., OCT imaging, biophysical measures of SC function, and inflammatory biomarkers provided a comprehensive set of parameters critical in strengthening our understanding of skin sensitivity and its associations with mechanical loading. The presented thesis addresses the difficulty in quantifying the skin-device interaction and provides a direction for selection of suitable skin measurement tools. This is particularly relevant for device manufacturers interested in developing skin-friendly products, accounting for the increasing demands for personalised solutions.

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Identifiers

ORCID for Peter Worsley: orcid.org/0000-0003-0145-5042

ORCID for Daniel L Bader: orcid.org/0000-0002-1208-3507

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