Emotional Rollercoaster: A Journey Through the Science of Feelings. Claudia Hammond

we all experience disgust at some time, the strength of the feeling can vary considerably. When Paul Rozin, a world authority on this emotion, measures sensitivity to disgust he finds at one end of the scale people who would be happy to eat live locusts, while at the other end there are people who are not prepared to blow their nose on a brand new piece of toilet roll due to its association with dirty toilets. Women tend to be at least 10-20% more sensitive to disgust than men and that sensitivity also changes over the lifespan, peaking in the teens and tailing off gradually towards old age. From an evolutionary perspective it has been argued that disgust decreases with fertility because a person no longer needs to keep themselves or their offspring healthy in order to continue the species. However, it could be simpler than that; perhaps we become inured to supposedly disgusting sights through caring for dependants. Moreover, as people reach adulthood they gradually worry less about other people’s perceptions, so you might expect a corresponding reduction in the fear that other people might find you or your behaviour disgusting.

      Ultimately, a little variation in our individual sensitivity to disgust doesn’t seem to matter and it’s unclear whether the most sensitive people do succeed in avoiding disease more successfully than others. An extreme excess of feelings of disgust can result in an obsessive-compulsive disorder (OCD) involving strict washing routines and lengthy rituals. A person might wash their hands in a precise order, even cupping water in the hand and splashing it over the taps to avoid recontamination when they turn the taps off. These rituals can become so time-consuming that they are disabling. A person might spend every morning scrubbing the kitchen to ensure that it’s definitely germ-free and, in time, might become unable to leave the house because nowhere else is sufficiently hygienic.

      The American movie mogul Howard Hughes became so obsessed with the avoidance of germs that he employed staff whose job it was to keep him from contamination. He devised precise rules such as using at least fifteen tissues to open the cabinet where he kept his hearing aid. Before handing him a spoon his servants had to cover the handle in tissue, seal it with tape and then wrap a second tissue on top. His obsession with dirt ruled his life, eventually leading him to live as a recluse.

      While researching the way the brain processes disgust, Mary Phillips wondered whether the people with this particular type of OCD might show differences in brain activity. She scanned the brains of people with and without the disorder whilst they looked at a series of pictures that most people would find disgusting, such as photos of filthy toilets and mutilated bodies. In amongst these she added some photos which only those with washing obsessions would be likely to find repulsive – a plate covered in tomato sauce, an unmade bed. The results were striking. The insula was activated in everyone when they saw the disgusting pictures, but it also lit up in people with OCD when they saw the harmless pictures of domestic untidiness. What we can’t tell from this experiment is which came first. Do the people with OCD have an overactive insula, causing them to feel the same degree of revulsion on seeing a dirty plate that the rest of us might feel when we see a dead animal? Or is it the other way around? Is the person so anxious about dirt that this is reflected in their brain activity? Dr Phillips’ forthcoming study might bring us closer to the answer. She’s planning to study people’s brains before and after treatment for OCD. Once they have recovered, the activity in the insula should, in theory, reduce. However, this still won’t tell us why the problem started or whether the insula can simply go wrong by itself.

      One curious finding was that people with OCD also have trouble spotting expressions of disgust in other people. This is surprising because you would expect those with a particular sensitivity to disgust to be alert to other people’s warnings that there’s something disgusting nearby.

      An over-sensitivity to disgust might also be implicated in some phobias. When people have irrational fears an element of disgust is sometimes involved. To compare a mild phobic situation with one of more rational fear, while the thought of a large spider makes me shudder with horror, the idea of being stranded, dangling from a rope on a steep mountainside does not make me feel revolted – although it does make my heart beat faster. And intriguingly, it has been found that people with a phobia of blood respond not with a fast heart rate as they would in other situations that scare them, but with the slowed heartbeat you would expect with disgust. Research has found that people who are afraid of spiders do tend to be at the higher end of the disgust sensitivity scale – with those more likely to be horrified at the idea of sharing a bottle of water, for example. In one experiment Peter De Jong from Maastricht University talked people through three scenarios. In the first you had to imagine you were a care assistant whose job it was to go into a room where an elderly man was vomiting, clean him up and change his shirt. As soon as you have finished he is sick again. In a second scenario you had to picture yourself descending some stairs into a cellar to fetch a bottle. Spiders’ webs hang from the ceiling and you duck as a web touches your face. You see a spider lowering itself down on a string and then feel something touch your neck. When you take a bottle out of the crate, you disturb a large spider which runs across your hand. The third situation was more pleasant; you are simply waiting to meet a friend at the station. During this guided imagery the experimenters recorded the extent to which each person moved their levator labii superioris – the sneering muscle which indicates disgust. It was found that the people who were phobic about spiders found the spider scenario the most disgusting. You might have expected them to be afraid, but instead their facial expressions showed disgust. Strikingly, spider phobics also scored higher on a scale measuring general sensitivity to disgust. It seems that spider phobia might actually highlight a fear of contact with something disgusting.