Review article The tongue microbiome: A gateway to systemic health and disease Marwan Mansoor Ali Mohammed a,*,1 , Sausan Al Kawas a,2 , Gamilah Al-Qadhi b,3 a Department of Oral and Craniofacial Health Sciences, College of Dental Medicine, Research Institute for Medical and Health Sciences, University of Sharjah, United Arab Emirates b Department of Basic Dental Sciences, Faculty of Dentistry, University of Science and Technology, Aden, Yemen A R T I C L E INFO Keywords: Tongue microbiome Tongue coating Tongue diagnosis Systemic conditions ABSTRACT Objective: In this review, we summarize the current state of the art of the tongue microbiome research and its potential as a diagnostic tool for different oral and systemic diseases. We discuss the methods used to charac- terize the tongue microbiome, the factors that influence its composition, and the potential mechanisms by which it may be linked to systemic diseases. Methods: A comprehensive literature search of articles on tongue microbiome from Jan 2010 to Jan 2024. Results: The majority of the studies reviewed demonstrated significant alterations in the tongue microbiome across various diseases and conditions. including chronic insomnia, rheumatoid arthritis, Sjogren syndrome, chronic hepatitis B, pneumonia, geographic tongue, post-menopausal osteoporosis, human immunodeficiency virus (HIV), diabetes mellitus, and pediatric inflammatory bowel disease. There are some conditions that show no significant changes in the tongue microbiome of patients compared to the healthy control like in children with autism and the young patients with chronic kidney disease and their healthy mothers. Conclusions: The microbiome of the tongue has been shown to be connected to the development and progression of different types of systemic diseases and conditions. 1. Introduction Tongue examination has been used for thousands of years in the diagnosis of different diseases in the human body [1]. This old tradition has been adopted from the Traditional Chinese Medicine (TCM) [1,2]. While there was a distinction between expert and novice diagnosticians, understanding the traditional Chinese medicine process opens possibil- ities for developing advanced analysis technologies and identifying the most effective practices in this context [2]. The tongue coating charac- teristics like thickness and color played a crucial role in disease diag- nosis as the dorsal surface of the tongue forms a rich habitat of microorganisms especially bacteria [3]. A recent review study by Li et al. showed the dominant tongue coating microbiota at each taxonomic level depending on the data from The Human Oral Microbiome Database (HOMD, http://www.homd.org/) [4]. Tongue-coating microbiota in healthy individuals at the phylum level included the following: Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Spirochaetes, Fusobacteria, and Synergistetes [4]. Several factors can influence and alter the tongue microbial community in terms of quantity, composition, and microbial diversity. These factors include surgical procedures, medication use, herbal medicine, diet, oral hygiene status, as well as lifestyle habits such as smoking and alcohol con- sumption [5–10]. Alterations in the composition of the tongue micro- biome have also been associated with various human diseases, including chronic insomnia [11], rheumatoid arthritis [12], Sjogren syndrome [13], chronic hepatitis B [14,15], pneumonia [16], geographic tongue [17], post-menopausal osteoporosis [18], human immunodeficiency virus (HIV) [19], diabetes mellitus [20–22], and pediatric inflammatory bowel disease [23,24]. There are some conditions that show no signif- icant changes in the tongue microbiome of patients compared to the healthy control like in children with autism [25] and the young patients with chronic kidney disease and their healthy mothers [26]. The potential use of the tongue-coating microbiome as a compre- hensive tool for characterizing the health status of patients, particularly * Corresponding author at: Department of Oral and Craniofacial Health Sciences, College of Dental Medicine, Research Institute for Medical and Health Sciences, University of Sharjah, United Arab Emirates E-mail addresses: mmmohammed@sharjah.ac.ae (M.M.A. Mohammed), sausan@sharjah.ac.ae (S.A. Kawas), gamilah.alqadhi@dentistry.cu.edu.eg (G. Al-Qadhi). 1 ORCID: https://orcid.org/0000-0002-7101-1239 2 ORCID: https://orcid.org/0000-0001-6118-4382 3 ORCID: https://orcid.org/0000-0002-6865-4866 Contents lists available at ScienceDirect Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology journal homepage: www.journals.elsevier.com/journal-of-oral-and-maxillofacial- surgery-medicine-and-pathology https://doi.org/10.1016/j.ajoms.2025.01.009 Received 7 February 2024; Received in revised form 25 December 2024; Accepted 17 January 2025 Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology xxx (xxxx) xxx Available online 22 January 2025 2212-5558/© 2025Asian AOMS, ASOMP, JSOP, JSOMS, JSOM, and JAMI. Published by Elsevier Ltd. All rights reserved. All rights are reserved, including those for text and data mining, AI training, and similar technologies. Please cite this article as: Marwan Mansoor Ali Mohammed et al., Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology, https://doi.org/10.1016/j.ajoms.2025.01.009