What is the behavioral immune system?

The Behavioral Immune System (BIS) evolved as a psychological defense mechanism that operates to prevent infections before they happen. It enhances our sensitivity to hygiene, signs of disease in others, and even indicators of otherness, such as someone being from a different tribe. This system helps us avoid potential sources of contagion through feelings of fear, disgust, and a tendency for avoidance. Interestingly, the BIS can lead to behaviors such as being overly cautious or showing misplaced fear, such as wearing a mask while driving alone or excessively avoiding public spaces like grocery stores during pandemics. The activation of this system is generally involuntary and serves as a first response to perceived threats of infection 1.

Another interesting aspect of the BIS is its resemblance to the immune response in its operation during crises, such as pandemics. It begins with a nonspecific broad reaction (akin to the body's innate immune response) and ideally becomes more targeted and informed (similar to the adaptive immune response). This system can sometimes malfunction, much like an autoimmune response in the body, where it may cause more harm than the actual threat, highlighting its potential for causing societal overreactions in the face of health crises 2. Similarly, it has been suggested that the exaggerated responses during the COVID-19 pandemic could be seen as an overreaction of the BIS, analogous to a cytokine storm in the immune system, where the response is potentially more damaging than the threat itself 3.