Cerumen as a Biomarker: Biological Composition, Clinical Utility, and Translational Prospects: A Narrative Review
Ashraf A. El-Faham *
Biochemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt.
Lara A. El-Faham
Faculty of Medicine, Memphis University, Cairo, Egypt.
*Author to whom correspondence should be addressed.
Abstract
Cerumen, the waxy secretion of the external auditory canal, has long been regarded clinically as little more than an occasional cause of impaction and conductive hearing loss. A growing body of multidisciplinary evidence now reveals cerumen to be a biochemically rich matrix whose molecular constituents — encompassing lipids, proteins, steroid hormones, volatile organic compounds, nucleic acids, and microbial communities — may faithfully encode a wide range of physiological and pathological states. This narrative review synthesises current knowledge from chemistry, genetics, environmental medicine, clinical toxicology, oncology, and microbiology to evaluate cerumen's emerging role as a non-invasive biomarker matrix. The literature informing this review was identified through searches of multiple bibliographic databases, including Web of Science, Scopus, PubMed, and Google Scholar. Field-specific resources were additionally consulted, comprising Chemical Abstracts (via SciFinder), the Toxicology Literature Online (TOXLINE) database, the Human Microbiome Project data portal, the OMIM (Online Mendelian Inheritance in Man) database, and the PharmGKB pharmacogenomics knowledgebase. Topics addressed include the glandular origins and macromolecular composition of cerumen; the pivotal influence of the ABCC11 single nucleotide polymorphism on cerumen phenotype and its pharmacogenomic and oncological implications; the utility of cerumen in environmental and occupational biomonitoring, forensic and therapeutic drug detection, and endocrine profiling; putative associations with systemic diseases such as inborn errors of metabolism, breast cancer, and neurodegenerative conditions; the ecological and diagnostic dimensions of the cerumen microbiome; and the analytical platforms available for cerumen interrogation. Methodological considerations relating to sample collection, pre-analytical handling, and the comparative merits of cerumen relative to established matrices such as blood, urine, hair, and saliva are examined throughout. The review identifies key translational challenges and argues that, with standardisation of collection and analytical methods, cerumen merits serious consideration within future precision medicine and biomonitoring frameworks.
Keywords: Cerumen, earwax, biomarker, ABCC11, non-invasive sampling, volatile organic compounds, cerumen microbiome, pharmacogenomics, environmental biomonitoring, precision medicine