OCD, Contamination, and the Disgust Affect

OCD can be a maladaptive reaction to disgust, discomfort, and unease.

Posted Apr 26, 2019

Andrew Seaman / CC BY-ND 2.0
"Grossed out"
Source: Andrew Seaman / CC BY-ND 2.0

Perhaps the most visible of all OCD symptoms are those related to the fear of disease.  The obsession with contamination, and the associated rituals of cleaning and washing, are easy for non-sufferers to identify—and not only because the sufferer’s distress is so obvious.  Discomfort related to contamination and infection is universal and has deep roots in human evolutionary psychology.  These emotions and behaviors evolved over geological ages as a vital survival system—and while it functions differently, this underlying machinery is the same in OCD suffers and non-sufferers alike.

The origins of this obsession lie with our prehistoric ancestors and their dangerous environment.  Some dangers, like predators or harsh weather, were easy to recognize, and our ancestors evolved straightforward behaviors to manage them—such as the “fight or flight” response.  But they also faced a different category of dangers that were far harder to notice or react to: the invisible threats of poisons, parasites, and viruses.  These dangers were invisible, undetectable, and could remain dormant for months after the initial contamination, making them difficult to avoid through simple cause-and-effect learning. 

And so, over generations, our ancestors adapted to such unusual threats with a very particular set of responses—what psychologists call the disgust affect.  First, our ancestors learned to recognize clues to the presence of contagions, obvious ones like bodily fluids, excrement, and corpses, but also subtler signals like the skin discoloration or subdued behavior of the infected.  When confronted with something offensive, they adopted behaviors such as flaring nostrils, curling lips, and stepping back—avoiding the danger and visually signaling others to avoid it as well.  And if they accidentally ingested a toxic substance, they developed nausea, gagging and vomiting to eject the substance from their bodies.  Those individuals genetically predisposed to recognize contaminating objects and strongly experience the disgust affect thus had an evolutionary advantage, and would pass their inherent disgust sensitivity (as well as health and cleanliness strategies) to their children.

The trick is that, while these are all good strategies for preventing disease, they don’t solve the fundamental problem of diagnosing the cause.  If you suffer from food poisoning, it might have been caused by your most recent meal, or the one before that, or anything you ate in the past forty-eight hours.  There’s no way to be sure.  Daniel Kelly, author of Yuck! The Nature and Moral Significance of Disgust writes that “the disgust response is equipped—understandably, given the nature of the adaptive problem—with a bit of a hair trigger.”  When you feel sick, it is very easy to become disgusted by anything that might have caused it.  And it only takes one bad experience to leave you permanently disgusted by something—a phenomenon Kelly calls “one-shot learning.”   Finally, once we’ve established a trigger for disgust, it’s very easy for that disgust to transfer to other objects, through physical contact, or even just thinking about it.  “A single drop of sewage can spoil an entire jug of wine,” Kelly observes, “but a single drop of wine doesn’t much help in purifying a jug of sewage.”

All of this adds up to a system that can incorrectly identify commonplace objects as life-or-death dangers, and instantly connect these objects with powerful and extremely unpleasant emotions and symptoms—creating associations that cannot be forgotten or unlearned once established.  Anything could make you sick, so everything should be treated as a possible source of contamination.  You only need to be infected once to get sick, so you always need to be actively protecting yourself.  Being sick could kill you, so anything disgusting must be treated as a fatal danger.  And, on top of all of that, just thinking about any of this can cause physical symptoms like gagging, cramping or nausea. 

It’s easy to see why this was such a powerful and effective system for keeping our prehistoric ancestors healthy—and how, today, this system can misfire to trigger visceral and terrifying obsessive thoughts about sickness and death.

OCD sufferers can feel alienated by their disorder, or even find themselves judged by others.  So it’s important to remember: Thoughts about disgust and contamination are not irrational or unnatural.  Everybody has them because they’re fundamental to our psychology, and a major reason for our success as a species.  Obsessive-Compulsive Disorder is a maladaptive reaction to these ordinary but unpleasant experiences of disgust, discomfort, and unease. Because the threat of contamination is so vague and nebulous, it can overwhelm you and inappropriately occupy your thoughts. 

But that doesn’t mean you’re “crazy.”  It means that, biologically and psychologically, you’re a human being.  And, for what it’s worth, that’s a pretty common diagnosis. 

Copyright, Fletcher Wortmann, 2019.

Author of Triggered:  A Memoir of Obsessive-Compulsive Disorder (St. Martin’s Press), named one of Booklist’s “Top 10 Science & Health Books of 2012.”

Read my Psychology Today blog:  Triggered


Ekman, Paul.  Emotions Revealed: Recognizing Faces and Feelings to Improve Communication and Emotional Life.  2nd edition.  St. Martins, New York, NY, 2007. 

Kelly, Daniel.  Yuck! The Nature and Moral Significance of Disgust.  Bradford MIT Press, Cambridge MA, 2011.