Most noteworthy, however, is that recent studies have found significant links between brain fog and inflammation associated with chronic illness. Now that’s not to say you’ll have a chronic illness if you experience brain fog, but it could well be responsible if you do experience days where you’re cognitively impaired.

A recent study by researchers at the University of Birmingham and the University of Amsterdam found that inflammation appears to negatively impact the brain's readiness to reach and maintain an alert state. Using 20 male volunteers, the researchers administered a salmonella typhoid vaccine that causes temporary inflammation against a placebo (water), then measured brain activity while the subjects performed attention tests. The results were anything but foggy: those with inflammation had their attention processes compromised, while those without inflammation weren’t affected. 

"These results show quite clearly that there's a very specific part of the brain network that's affected by inflammation… This could explain ‘brain fog’," says Dr. Ali Mazaheri, a senior author of the study[2]. Similarly, 2 other studies - one conducted in 2013 [3] and the other in 2018 [4], both found significant increases in cognitive impairment among patients with Rheumatoid Arthritis - a chronic illness which causes severe joint inflammation.