People have long observed fog as a low-visibility phenomenon, but few realize that it is an atmospheric event closely linked to air quality. When fog transforms into smog, it becomes a vehicle for harmful air pollutants, significantly impacting human health. This chapter aims to trace the historical significance of fog, from the medieval miasma theory to modern epidemiological studies, by examining its multifaceted effects on human health, its role in trapping hidden air pollutants, mechanisms of acute and chronic exposure, and its broader implications for transportation. Fog-related air pollution exacerbates respiratory conditions like asthma and increases risks of acute infections, particularly in children and the elderly. Emerging research highlights potential carcinogenic risks and the need to study fog’s role in diseases such as asthma, chronic obstructive pulmonary disease (COPD) and vector-borne illnesses within the context of climate change. Advanced studies and integrated policies are essential for addressing fog-related health impacts and mitigating its effects as part of broader climate action strategies.