From environmental occurrence to human exposure: multisystem toxicity, immune-relevant mechanisms, and gaps in health-risk assessment of liquid crystal monomers

Liquid crystal monomers (LCMs), functional constituents of liquid crystal displays, are emerging contaminants increasingly detected in environmental and human matrices, yet the implications of these exposures for human health remain uncertain. This review critically synthesizes current evidence on environmental occurrence and potential exposure pathways, human biomonitoring, toxicokinetics, multisystem toxicity, immune-relevant mechanisms, and health-risk assessment gaps. PubMed, Web of Science Core Collection, and Scopus were searched from database inception to 22 July 2026. Forty-one primary studies met the predefined eligibility criteria, while additional environmental-occurrence studies were used to contextualize sources, release processes, and potential exposure pathways. LCMs have been reported in dust, airborne particulate matter, soils, sediments, and landfill leachate, indicating several plausible exposure pathways, including dust ingestion, inhalation, dermal contact, and dietary intake. LCMs have been detected in urine, serum, human milk, maternal serum, and cord serum, indicating exposure in the general population and during sensitive life stages. Experimental studies report neurological, hepatic, renal, intestinal, respiratory, cutaneous, endocrine, reproductive, developmental, and metabolic effects. Oxidative stress, inflammatory signaling, nuclear receptor perturbation, metabolic dysregulation, and gut microbiota disruption provide biological plausibility for immune-related effects, although direct evidence of classical immunotoxicity remains limited. Major uncertainties include heterogeneous analyte coverage, insufficient human toxicokinetic data, limited chronic low-dose and mixture studies, and the absence of congener-specific reference values. Future research should prioritize harmonized biomonitoring, environmentally relevant mixture testing, prospective studies in susceptible populations, and integrated risk-assessment frameworks for this emerging class of contaminants.