Can air pollution weaken your immune system?

Air pollution does not weaken your immune system in one simple direction. It throws it off balance instead. Fine particles and exhaust fumes activate pro-inflammatory immune cells, including a type of white blood cell that normally clears bacteria (neutrophils) and cells that drive allergic reactions. At the same time, the immune system's ability to fight viruses declines. You are therefore simultaneously more susceptible to excessive inflammatory responses and less well protected against viral infections.

For children the risk is greater, and it begins even before birth. Pregnant women who inhaled more fine particles gave birth to babies whose immune cells produced fewer signalling proteins immediately after birth. Those babies also had fewer T-cells, the immune cells that play a central role in protection against infection. After birth, exposure to fine particles is associated with higher IgE levels, a measure of allergic sensitivity. There are therefore sensitive periods during which air pollution can do the most damage to the developing immune system.

Over the longer term, air pollution has been linked in multiple studies to hay fever, allergic sensitisation, asthma and autoimmune diseases. Urban traffic plays a striking role in this: the effects are already visible at concentrations that are commonplace in many cities today.

Is there anything you can do about it? Vitamin D supplementation has been studied immunologically as a possible form of protection, but the evidence for this is currently too thin for concrete recommendations. What does help is limiting exposure: keeping windows closed near busy traffic, using indoor air purifiers, and for pregnant women avoiding areas with heavy traffic concentrations are the most direct practical steps.