The Microbiota, Immunoregulation, and Mental Health: Implications for Public Health

Christopher A. Lowry, David G. Smith, Philip H. Siebler, Dominic Schmidt, Christopher E. Stamper, James E. Hassell, Paula S. Yamashita, James H. Fox, Stefan O. Reber, Lisa A. Brenner, Andrew J. Hoisington, Teodor T. Postolache, Kerry A. Kinney, Dante Marciani, Mark Hernandez, Sian M.J. Hemmings, Stefanie Malan-Muller, Kenneth P. Wright, Rob Knight, Charles L. RaisonGraham A.W. Rook

Research output: Contribution to journalReview articlepeer-review

91 Scopus citations


The hygiene or “Old Friends” hypothesis proposes that the epidemic of inflammatory disease in modern urban societies stems at least in part from reduced exposure to microbes that normally prime mammalian immunoregulatory circuits and suppress inappropriate inflammation. Such diseases include but are not limited to allergies and asthma; we and others have proposed that the markedly reduced exposure to these Old Friends in modern urban societies may also increase vulnerability to neurodevelopmental disorders and stress-related psychiatric disorders, such as anxiety and affective disorders, where data are emerging in support of inflammation as a risk factor. Here, we review recent advances in our understanding of the potential for Old Friends, including environmental microbial inputs, to modify risk for inflammatory disease, with a focus on neurodevelopmental and psychiatric conditions. We highlight potential mechanisms, involving bacterially derived metabolites, bacterial antigens, and helminthic antigens, through which these inputs promote immunoregulation. Though findings are encouraging, significant human subjects’ research is required to evaluate the potential impact of Old Friends, including environmental microbial inputs, on biological signatures and clinically meaningful mental health prevention and intervention outcomes.

Original languageEnglish (US)
Pages (from-to)270-286
Number of pages17
JournalCurrent environmental health reports
Issue number3
StatePublished - Sep 1 2016


  • Anxiety
  • Depression
  • Lactobacilli
  • Microbiome
  • Mycobacteria
  • Posttraumatic stress disorder

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Nature and Landscape Conservation
  • Management, Monitoring, Policy and Law
  • Health, Toxicology and Mutagenesis


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