Earwax, medically termed cerumen, is a specialized lipid secretion produced in the outer third of the external auditory canal. It serves as a multifunctional protective barrier by combining glandular secretions with desquamated keratinocytes and hair. Cerumen exhibits wet (sticky, yellow-brown) or dry (brittle, gray-white) phenotypes, determined largely by ABCC11 gene polymorphism, with the dry type prevalent in East Asian populations (~80–95%).
Chemical Composition
Cerumen is composed of approximately 60% keratinized squamous cells, alongside 12–20% long-chain fatty acids (saturated C14–C26, unsaturated C18:1), 6–9% cholesterol, squalene, and aliphatic alcohols. These components originate from secretions of ceruminous glands (modified apocrine sweat glands) and sebaceous glands.
Proteomic studies reveal the presence of antimicrobial peptides such as lysozyme, lactoferrin, LL-37, β-defensins, and SLPI, which account for 10–15% of the protein content and provide innate immune protection. Wet-type cerumen contains higher proportions of squalene and cholesterol esters, whereas dry-type cerumen shows elevated keratin content.
Physical Properties
Wet cerumen is typically tacky, with a pH ranging from 5.2 to 6.5 and a specific gravity close to 1.0. Its yellow-orange coloration results from oxidized carotenoids. In contrast, dry cerumen flakes easily due to reduced viscosity.
Both cerumen types migrate laterally through jaw motion and epithelial peristalsis at an average rate of ~0.1 mm/day, allowing natural self-expulsion. Analytical GC-MS hydrolysis identifies palmitic and stearic acids, confirming the lipid-rich matrix.
Biosynthesis and Genetics
Ceruminous glands (approximately 100–200 per auditory canal) secrete lipid-rich apocrine fluid that mixes with sebum and migrating epithelial debris. The ABCC11 A allele (538G>A SNP) disrupts fatty acid transport, producing dry cerumen with about 50% lower lipid content and increased lysozyme levels.
Cerumen production varies with age (peaking during adolescence), diet (ω-6 fatty acids promote wet-type secretion), and environmental exposure, as dust can accelerate turnover.
