The Acari Hypothesis, VIII: the human apocrine-mammary-microbiota axis and Staphylococcus epidermidis mutualism

Human integument is unusual among primates for its expanded eccrine network, glandular specialization, acidic surface pH, and enrichment of staphylococcal taxa. Framed within the Acari Hypothesis, this manuscript proposes a unifying apocrine-mammary-microbiota axis in which human integumentary glands cultivate protective symbionts, with Staphylococcus epidermidis as a keystone. Reviewed evidence encompasses acid mantle biochemistry and glandular antimicrobials that favor acid- and lipid-tolerant staphylococci while restricting pathogens and possibly ectoparasites. Mammalian apocrine secretions rely on microbial metabolism to convert precursor molecules into bioactive compounds that mediate species-specific physiological functions. This reliance may be consistent with the enrichment of staphylococci at apocrine-rich sites in humans. Mammary biology indicates vertical transfer of skin- and milk-associated microbes that stabilize epithelial ecosystems across generations. The manuscript develops a mutualist model for S. epidermidis on human epithelia, reconsiders device-associated infections, and surveys staphylococcal dysbiosis across dermatologic conditions. As proposed, human integumentary and mammary glands co-evolved to cultivate and vertically transmit symbiotic staphylococci, whose metabolites and niche competition defend against ectoparasites and pathogens while balancing epithelial and metabolic homeostasis.