The air we breathe harbors an invisible but potent threat: particulate matter, especially ultrafine particles (UFPs) less than 100 nanometers in diameter, which are increasingly implicated in brain health. Long recognized for their impact on the respiratory and cardiovascular systems, these nano-sized pollutants have recently emerged as key players in neurodevelopmental and neurodegenerative disorders. This review delves beyond the well-known respiratory impacts, unravelling the cellular and molecular effects orchestrated by these airborne pollutants within the brain. We mapped diverse entry routes that seem unexpected: from a direct translocation via olfactory and trigeminal nerves, through compromised blood-brain and lung-blood barriers, to emerging pathways like the gut-brain axis and even placental transfer affecting the developing fetal brain. Once inside the brain, those particles disrupt the cellular and molecular harmonized pathways by altering redox homeostasis, compromising mitochondrial function, and activating glial cells toward pathological phenotypes. Outstandingly, we explore the complex journey of airborne pollutants from inhalation to neural deposition, highlighting evidence for the physical presence of particles in human brain tissues and presenting insights into the brain’s nascent clearance systems. Notably, the polluted air around us may leave behind more than respiratory scars; its nanoscopic footprints could be etched deep within our neural networks across the lifespan. Finally, we propose future research directions, emphasizing mechanistic studies, and targeted protection of vulnerable populations to safeguard cognitive health.