Archaeal key-residents within the human microbiome: characteristics, interactions and involvement in health and disease

•Archaea have been established as abundant and prevalent microbial components of host microbiomes.•Not a single archaeal pathogen has yet been identified and archaeal microbiome components remain understudied.•Methanobrevibacter, is represented by two major species, which modulate the host’s nutrient break-down.•Methanosphaera is detected by the human immune system and might be involved in pathogenic processes.•The role of other host-associated archaea, remains to be further elucidated in future studies.