Susceptibility

Susceptibility refers to the effects of biological inequity on the human immune response, specifically the fact that persistent environmental stressors on a community place these individuals at a heightened risk of developing severe symptoms and chronic illnesses compared to a normative population, not exposed to significant stressors.

Saez and Lopez-Casasnovas (2019) presented a comparative study on the susceptibility of a deprived vs wealthy neighbourhood in Barcelona to pollution. The results indicated that the deprived neighbourhood was significantly more at risk of dying (30% higher probability) from environmental health hazards, such as air and noise pollution, than the wealthy neighbourhood.

This increased susceptibility was due to a mixture of other psychosocial stressors that the deprived neighbourhood was already experiencing: low income and poverty, low quality of housing and low access to services. Another study (Rosa et al., 2019) showed compelling evidence of a relationship between prenatal stress and onset of asthma in children.

Children born to mothers who experienced high psychosocial stress (eg. divorce, health concerns etc), were significantly more at risk of developing asthma later on in life; the risk further increased when the mothers were also exposed to higher air pollution levels (Rosa et al., 2019).

Expanding on this, Landeo-Gutierrez et al. (2019) argue that certain types of psychosocial stressors, such as exposure to violence and crime, increased the risk of onset of asthma, especially when in co-presence with air pollution. In particular, they found a strong correlation between post-traumatic stress disorder (PTSD) and asthma onset.

The Biological Mechanisms of Susceptibility 

At the crux of this theory is that when the body is faced with stressors it adapts through a process called allostasis, which means “achieving stability/homeostasis through change”. Chronic HPA-axis activation due to constant psychosocial (financial insecurity) and environmental stressors (air pollution), combined with maladaptive behaviours such as poor sleep due to shift work, can impede the allostatic process.

This creates ‘allostatic load’, which is “wear and tear” on biological systems that communicate with the stress response, resulting in increased systemic inflammation, and compromised immune and metabolic systems. In the long run, this can leave people more susceptible to the health risks of environmental toxins like air pollution.