In moderation, religious and spiritual practices can be great for a person’s life and mental well-being. But religious fundamentalism—which refers to the belief in the absolute authority of a religious text or leaders—is almost never good for an individual. This is primarily because fundamentalism discourages any logical reasoning or scientific evidence that challenges its scripture, making it inherently maladaptive.

It is not accurate to call religious fundamentalism a disease, because that term refers to a pathology that physically attacks the biology of a system. But fundamentalist ideologies can be thought of as mental parasites. A parasite does not usually kill the host it inhabits, as it is critically dependent on it for survival. Instead, it feeds off it and changes its behavior in ways that benefit its own existence. By understanding how fundamentalist ideologies function and are represented in the brain using this analogy, we can begin to understand how to inoculate against them, and potentially, how to rehabilitate someone who has undergone ideological brainwashing—in other words, a reduction in one’s ability to think critically or independently.