An important paper from several prominent members of the microbiome and health research community, including Fergus Shanahan and Graham Rook. They are not arguing that we should disregard the rapidly-accumulating mass of research which links our gut microbiome with mental and physical health – far from it – but we should divorce it completely from naive reporting that suggests personal hygiene and hygiene in the home should be moderated because it directly leads to our modern plagues of autoimmunity and allergy – and “a little bit of dirt works wonders for your health”. Domestic hygiene is vital to protect against pathogens, they argue, while microbiome engineering through things like probiotics, will give all of us healthy diversity of “friendly” microorganisms in our guts and elsewhere. This is all to do with re-naming the “hygiene” hypothesis the “old friends” hypothesis. The link leads to the abstract of their paper. You will have to rely on your institution’s subscriptions – or the library – to go further!