What is your skin barrier anyway? The skin barrier is the outermost layer of skin cells (a.k.a. the stratum corneum). It's also home to the lipid matrix which is made up of ceramides, cholesterol, and fatty acids. The function is to protect the skin from environmental irritants, free radicals, and pathogens. It also helps to prevent transepidermal water loss (TEWL). Think of your skin barrier as a “brick wall.”