Disgust, in its most familiar form, is our response to something vile in the world—spoiled food, a dirty floor or rats cavorting in the subway. It is a contamination-avoidance mechanism that evolved to help us make biologically adaptive decisions in the heat of the moment. Yet disgust has also come to have powerful symbolic elements. When left unchecked, these symbolic qualities can have devastating impacts on our mental states.

Consider, for example, the often dramatized, heartbreaking image of a woman crouched in the corner of a shower and frantically trying to scrub her body clean after being raped. Empirical evidence supports the characterization. Seventy percent of female victims of sexual assault report a strong impulse to wash afterward, and a quarter of these continue to wash excessively up to three months later.

For women, simply imagining an unwanted advance can turn on this moral-cleansing effect. Psychiatrist Nichole Fairbrother of the University of British Columbia Hospital and her colleagues looked more closely at the phenomenon of mental pollution in a study published in 2005. Two groups of female participants were told to close their eyes and picture being kissed. The members of one group were instructed to imagine being aggressively cornered and kissed against their will. The members of the other group were asked to envision themselves in a consensual embrace. Only those women in the coercive condition chose to wash up after the study. In many cases, it seems as though a person's sense of self has become contaminated.

When symbolic disgust gets into one's core identity, the psychological sanitation process is never an easy one. Residual grime clouds the subjective filter through which a person perceives herself. If left untreated, these effects can permanently darken and sully her entire sense of being.

The Immoral Self
Disgust in its more typical forms generates feelings of hatred and loathing of others. Those emotions lead to a behavioral avoidance of the object of one's social distaste. In fact, the measurable physical distance placed between oneself and the hated target, such as in an elevator, can show this effect empirically. No matter how our worldview tilts, we usually do not stand too close to people whom we believe harbor opinions that are morally repellent to us. Nor do we seek to place ourselves in the immediate vicinity of those who have engaged in social behaviors we strongly believe are offensive and wrong.

Avoiding such a morally aversive person gets far more complicated, however, when the primary source of your symbolic disgust is you. After all, there are only three ways to escape the self—depressive sleep, drugs and suicide. Needless to say, none of these options is healthy.

Once a person feels tainted in this way by an act judged to be especially unacceptable by his or her own society, either as the victim of the act or as the offender who feels genuine shame and remorse, these rankling feelings of symbolic disgust can quickly metastasize into malignant self-hatred. Sexually abused children, for example, are far more likely than their peers to develop an exhaustive suite of psychopathologies later in life. Suicide rates skyrocket, and correlations have been found with everything from chronic depression to self-harm (such as cutting), substance abuse, eating disorders, paranoia, hostility and psychoticism.

The most common way of managing the damage is to channel the harmful, caustic emotions elsewhere. Usually this method involves directing the symbolic disgust outward—away from the self—and toward those perceived to be responsible for sullying the self. A 2002 study led by psychologist George Bonanno of Columbia University, for instance, showed that the coping strategies of adults who had been sexually abused as children could be reliably gauged by observing their facial displays during a therapy session.

The researchers looked at two expressions of happiness, referred to as Duchenne and non-Duchenne smiles. Named after a 19th-century neurologist, the Duchenne smile conveys genuine pleasure and engages both the mouth and the eyes, whereas a non-Duchenne smile is linked with concealment and social politeness. Bonanno and his colleagues found that those who, as kids, had not disclosed their sexual abuse to others (for example, it was discovered by another adult and only then reported) and who blamed themselves displayed far more non-Duchenne smiles than did those survivors who blamed their abusers. This latter group was more clearly identifiable by their facial expressions of disgust—a palpable moral loathing—whenever speaking about those who had harmed them.

Disgusting to Whom?
Although such powerful symbolic disgust responses are all too real in the damage they can do to a person's well-being, you may be surprised to learn that their precise parameters have no basis in a moral reality. Human beings have evolved to combat pathogens through adaptive responses that require absolutely no enculturation. We do not have to learn how to vomit, for instance, after wolfing down a burger infected with E. coli. The symbolic disgust response, in contrast, emerges from prevailing cultural forces. What might have made a Japanese person commit ritual suicide in the 18th century because he could not stand to live with himself and his social offense would for most of us today be quickly forgotten as a trifling incident. Given their sheer emotional intensity, it is easy to mistake feelings of symbolic disgust for an immovable moral reality that exists outside our own subjective head. But no such reality exists.

Anthropologists have long known just how easy it is to make Western moral compasses spin out of control by describing other so-called exotic cultural traditions, especially those involving sex. Consider one elaborate ritual in Papua New Guinea, described by anthropologist Gilbert Herdt, now at San Francisco State University. In the tribe he called the Sambia, boys close to their eighth or ninth birthday are banished to a bachelor's hut filled with older males whom they must fellate. The Sambia believe that the ritual transforms their youths into mighty soldiers. In our society, this ritual would be unspeakable, causing irreparable harm and condemning these boys to lifelong issues with their sexuality. In contrast, Sambia adults and older teenagers who participate are seen as altruistic. The Sambia perceive harm in denying boys participation in the ritual because doing so would permanently brand these children as weaklings who would be judged unworthy of defending the community as adult warriors.

The notion of abnormal sexuality is as much a matter of straying from our culture's script as it is one of violating the laws of reproductive biology. This is not to excuse or downplay the violence done to victims of abuse but to note that the concept of perversion or going against what is right is a phantom of the moralizing human mind.

Oddly enough, a healthy dose of moral nihilism is the antidote for so many of the social ills connected to human sexuality. To adopt the most clear-sighted stance on these increasingly slippery subjects, we must remember to take deviance within its given context, and harm must be understood as harm experienced by the parties involved, not by us as “disgusted” onlookers.

Morality is not out there in the world; it is a way of seeing, and it is constantly evolving. The emotional atmosphere of our own culture has undergone radical social climate changes. To assume we are now finally glimpsing a clear moral reality that previous generations did not would be stupendously foolish of us.