One vascular network that you certainly don’t want to mess with is the blood-brain barrier. This barrier keeps your damage-prone brain safe from chemicals in your blood that might harm it. Unfortunately, PM2.5 has been shown to cause blood-brain barrier dysfunction in young people and even promote the appearance of the two hallmarks of Alzheimer's disease. And disruption of this barrier isn’t just linked to Alzheimer’s disease; autism, multiple sclerosis, epilepsy, and Parkinson’s disease are all associated with blood-brain-barrier dysfunction.
One tiny PM2.5 particle is called magnetite. Magnetite is made of iron and is commonly found in the air of big cities. When we breathe it in through our noses, it's able to enter the body and travel up to the brain. Once there, it can "infect" multiple regions including the memory-processing hippocampus, which is among the first structures to be damaged in Alzheimer’s disease. Shockingly, these nanoparticles have been discovered in the brains of children as young as 3, causing inflammation and impaired cognitive function.
So can pollution actually cause dementia to develop? That’s an unknown at this time, but given all of the research above, it would seem plausible at the very least. One study, which sought to answer this very question, found that residing in an area with high levels of air pollution increased risk of cognitive decline by 81 percent and Alzheimer's disease by 92 percent. In fact, 20 percent of Alzheimer's cases may be due to exposure to high levels of fine particulate matter. (These are correlational figures, which would need to be validated by further research.)