The sticky situation of human skin

The largest organ of the body, namely the skin, is a three-layer system composed of the epidermis, dermis, and subcutaneous tissue (Venus et al. 2010; Yousef et al. 2025). The outermost epidermis maintains the skin barrier and produces new skin cells and melanin. The middle layer, the dermis, contains glands, nerves, and blood vessels, providing strength and flexibility to the skin. The deepest fatty layer acts as the bridge between skin and underlying tissues. As with the gut microbiome, there is a plethora of microbes including bacteria, fungi, and viruses residing in the different layers of the skin, making up the skin microbiome (Chen and Tsao 2013; Swaney and Kalan 2021; Khan and Koh 2024). Skin microbiome composition varies by body site (Perez Perez et al. 2016; Bjerre et al. 2021) and factors such as age (Luna 2020), genetics (Si et al. 2015), and immunity (Belkaid and Segre 2014; Peroni et al. 2020). This diverse microbial ecosystem faces off challenges from invasive pathogens (Nakatsuji et al. 2021) and environmental aggressors such as some soaps (Mijaljica et al. 2022), UV radiation (D'Orazio et al. 2013; Tang et al. 2024), pollutants (Bocheva et al. 2023), and changes in temperature and humidity (Engebretsen et al. 2016).