Seafood formaldehyde: From endogenous biochemistry to adulteration detection and human health risk

Formaldehyde in seafood may arise endogenously during post-mortem biochemical changes in susceptible fish or through external formalin treatment, complicating food authenticity assessment, exposure evaluation, and regulatory enforcement. This narrative review synthesized literature published from 1953 to 2025 and proposes a novel source-to-risk framework that integrates biochemical formation, analytical measurement, source attribution, dietary exposure, and regulatory interpretation. Unlike previous reviews focused primarily on occurrence, adulteration, detection methods, or legislation, it distinguishes three questions: whether formaldehyde is present, whether its origin can be established, and what health risks may follow. The framework integrates species susceptibility, storage history, free and bound formaldehyde, analytical limitations, and supply-chain traceability. Selected fish systems document endogenous formation associated with trimethylamine N-oxide (TMAO) demethylation, but this cannot be generalized across seafood. Colorimetric and ultraviolet–visible methods support accessible screening, whereas high-performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC-MS) offer more selective laboratory analysis. Emerging technologies, including portable Raman spectroscopy coupled with deep learning, require independent, matrix-specific validation. Market surveys alone cannot prove intentional adulteration or population-wide prevalence. The proposed tiered pathway combines screening, confirmation, contextual source assessment, exposure estimation, and jurisdiction-specific regulatory evaluation, highlighting priorities for species-specific reference data, validated attribution models, and reliable surveillance.