Ex Vivo Assessment of Heat and Humidity Effects on Human Skin and Potential Protection by Kombucha Tea Extract

Human skin homeostasis relies on the delicate equilibrium between epidermal stem cell renewal, dermoepidermal junction (DEJ) architecture, and environmental interactions. With aging and exposure to external stressors, this equilibrium becomes disrupted, leading to reduced regenerative capacity. In this study, we established an ex vivo human skin model to examine the impact of dry and tropical (hot and humid) environmental conditions on epidermal homeostasis and to evaluate the protective potential of Kombucha tea extract, a fermented tea known for its antioxidant and regenerative properties. Histological analyses revealed that tropical conditions induced pronounced epidermal thickening (+157%) and disruption of the normal undulating architecture of the DEJ. Atomic force microscopy demonstrated a loss of mechanical contrast between dermal papillae and epidermal ridges, indicative of junctional flattening (−61 and −81%). At the molecular level, heat and humidity upregulated a stem cell marker (+85%) and collagen VII (+39%), reflecting an adaptive but potentially destabilizing activation of basal keratinocytes and matrix reorganization. Topical application of Kombucha tea extract counteracted these effects. Together, these results highlight the sensitivity of epidermal stem cell niches to heat and humidity stress and identify Kombucha tea extract as a promising bioactive agent to preserve epidermal homeostasis under challenging climatic conditions.