Healthy skin has healthy microbiota: how can we help?

Knowledge is lacking on the exact composition of the skin microbiota and the exact mechanisms with which it interacts with the skin. Virtually every day new species of microorganisms are discovered on the skin. Some species are associated with skin diseases. A well-known example is Staphylococcus aureus (S aureus) which plays an important negative role in the pathophysiology of atopic dermatitis. Propionibacterium acnes, now called Cutibacterium acnes (C acnes), is another species which is associated with a skin disease, in this case acne. Staphylococcus epidermidisis another well-known species, considered as one of the ‘good’ microbes on the skin. Many other species live on and in the skin, though, and is S epidermidis really just ‘good’?

Are ‘good’ microbes good?

‘The dose makes the poison’. This does not just go for ‘molecules’, but also for microorganisms. No species can be considered 100% harmless.S epidermidis, commonly recognized as ‘good’, is only good at a low enough dose and on intact skin. It can be considered to be a so-called ‘pathobiont’. On compromised skin it can trigger severe adverse effects. The application of Sepidermidison sterilized skin leads to severe disruption of the quality of skin and barrier function. On the other hand, one of the predominant microbes living on oily skin, Cutibacterium acnes, is a commensal skin bacterium which is not always necessarily a pathogen. It can safely be concluded that there is no such thing as ‘good’ and ‘bad’ bacteria. We should rather consider a ‘healthy’ or ‘unhealthy’ mix of microorganisms. Healthy, non-diseased skin, shows a ‘healthy’ (‘not unhealthy’, at least partly ‘mutualistic’) mix, whereas with many skin diseases it is clear that the mix of microbes is unhealthy (at least partly pathogenic).