TNF and major depressive disorder: Air pollutants potentially play a role in mental health problems by inducing neurotoxicity, neuroinflammation and hormonal dysregulation.9 All of these mechanisms have been found to potentially act over short time frames.1 In particular, short-term exposure to PM10 is associated with the increased levels of cytokines (including interleukins 1-beta (IL-1β) and 6 (IL-6) and tumour necrosis factor alpha (TNF-α)) found in people with depression.