Humans have evolved a symbiotic relationship with ‘good’ bacteria over the millions of years that both have been around. The gut is the most heavily colonised spot, where bacteria assist in the digestion process and help to regulate immune function, and in return siphon off a tiny proportion of the nutrients they help to release. The skin, which represents a major practical barrier that protects you from your environment, is also colonised by bacteria, which sit on the outer skin layer, and in sebaceous glands and hair follicles. Researcher’s at the National Instutite of Allergy and Infectious Diseases in Bethesda, USA, have shown for the first time that skin-bourne bacteria play a major role in helping to control the patrolling immune cells that are poised to respond to pathogenic invasions. Local skin immune responses to the protozoan parasite, Leishmania major, were much more robust and protective in colonised mice (who had the helpful bacteria, Staphylococcus epidermidis, on their skin) compared to germ-free mice (who had no helpful bacteria on the skin). So, treat your skin gently, and protect your caring, sharing bacterial communities.

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Naik S, Bouladoux N, Wilhelm C, Molloy MJ, Salcedo R, Kastenmuller W, Deming C, Quinones M, Koo L, Conlan S, Spencer S, Hall JA, Dzutsev A, Kong H, Campbell DJ, Trinchieri G, Segre JA, & Belkaid Y (2012). Compartmentalized control of skin immunity by resident commensals. Science (New York, N.Y.), 337 (6098), 1115-9 PMID: 22837383