Irritant contact dermatitis: beyond a diagnosis of exclusion.

Irritant contact dermatitis (ICD) is the most common form of contact dermatitis and a leading cause of occupational skin disease, but remains underrecognized relative to allergic contact dermatitis (ACD). Direct chemical or physical injury to the epidermal barrier causes ICD, which can develop in anyone when exposure intensity or duration exceeds the skin's repair capacity. ICD is increasingly understood to involve more than barrier disruption: it is an innate immune-mediated inflammatory disorder involving keratinocyte-derived cytokines, neutrophil recruitment, C-C motif chemokine ligand 2-C-C motif chemokine receptor 2-interleukin-1β signaling, Toll-like receptor 3, and inflammasome activation. Host factors, particularly atopic dermatitis and filaggrin loss-of-function variants, further influence susceptibility. Clinical phenotypes range from acute irritant reactions to chronic cumulative dermatitis, and occupational wet work is a major preventable exposure. Distinguishing ICD from ACD is difficult because their clinical and histopathological features overlap, they may coexist, and ICD-related barrier damage may facilitate subsequent allergic sensitization. Diagnosis therefore requires assessment of exposure history, lesion distribution, symptom quality, and temporal course, with patch testing when ACD is suspected. Molecular biomarker panels and noninvasive imaging or barrier-assessment techniques may improve diagnostic precision, but remain investigational. Management should prioritize identifying and removing irritants, reducing exposure, implementing appropriate protective measures, and restoring the epidermal barrier. Recognizing ICD as a distinct clinical entity, rather than simply a diagnosis of exclusion, is essential for accurate diagnosis and effective management of contact dermatitis in clinical practice.