Our environment is the niche of billions of bacteria, forming a real ecosystem. Some of these microorganisms are essential contributors to human health. Our body harbours itself billions of microorganisms at different mucosal levels. The skin is also the place of important microbial diversity. Mrs Maxence de Villemeur and Dr Christian Sanchez at Lallemand Pharma discuss how this microbial community interact with each other, but also with their host, developing a real symbiosis to enhance natural defences.