Barrier Function

As everyone had heard by now the skin is our largest organ, measuring in at 1.8 square meters and supporting an astonishingly wide variety of habitats. It also is home to approximately one trillion microorganisms of about a thousand different species, including bacteria, fungi, viruses, and even mites (Demodex).

The skin microbiome is often compared to the gut microbiome, though upon closer inspection the comparisons don’t quite run in parallel. The major dissimilarity is that unlike the gut, which offers an almost ideal environment for the growth of fermentative bacteria, the skin is vast expanse of inhospitable territory. Much of it can be likened to the Great Salt Lakes area; dry, salty, acidic and nutrient poor. Think elbows, knees, legs and arms for example. However, what stands out on the skin map, with its variety of distinct ecosystems resulting from conditions which favor different subsets of organisms, is the populous nature of the facial area. It’s like looking at an urban center surrounded by swathes of countryside dotted here and there with small towns. The urban area is clearly the cool place to be; it is thriving with different species of microbes, fungi and mites; lipophilic microbes such as Cutibacterium acnes spp, fungi like Malassezia spp, as well as the Demodex mite in the hair follicles of the eyelashes. On a side note, the Demodex mite is known for its vigorous, some might even say debauched, night life— next time you go dancing at a crowded club it would be fun to imagine that you’re a Human Demodex who’s ventured out of your hair follicle for a night on the town. In any case the facial area, and to some extent parts of the back, are the regions where we can expect to see different species of microorganisms thriving and in abundance, sometimes beyond what we might like; for example if you’re a teenager dealing with breakouts you most likely have an overcolonization of a strain of Cutibacterium acnes that can cause acne.

The good news is that most of the microorganisms inhabiting these regions are commensal, i.e. harmless, while those that are symbiotic, like Staphylococcus epidermidiswhich keeps pathogens like Staphylococcus aureus in check, are working tirelessly to keep you healthy. Even the human Demodex mite is just a nuisance to most people, though it is associated with rosacea in folks where the mites tend to get out of hand—with rosaceans playing host to about fifty per cent more Demodex than non-afflicted people.

In our recent post about supporting your skin’s barrier function, we expressed some highly opinionated thoughts on exfoliation. (We called it a “disaster that disrupts your skin’s natural processes.”) We stand by those words! But it’s complicated, so we wanted to give a bit more context.