Animals do not have a problem with it. Small children even play with it. So why are adult humans so disgusted by faeces? Ayesha Nunhuck investigates

Until my second year as a medical student, I was only familiar with aversion to faeces as some sort of humour. But the aversion is widespread: why are we so disgusted by our own excrement?

Valerie Curtis of the London School of Hygiene and Tropical Medicine believes rejection of bodily secretions, such as faeces, may be a biological mechanism for avoiding infectious disease (Anatomy of Disgust, Channel 4, 2000). More than 1011 bacteria are found in each gram of dry faeces; 40%-50% of the dry weight.1­3 Also, infected individuals excrete high numbers of viruses, such as cholera and typhoid.4 5 Generally, contamination by human excrement is regarded as the greatest risk to water supplies, with a huge resultant morbidity and mortality worldwide.5 6

When and how humans became averse to faeces is not known. One proposal is that our ancestors distancing themselves from faeces was to aid survival by concealing their scent from predators.7 Bacteria in the intestine and faeces ferment carbohydrate residues releasing volatile fatty acids and pungent compounds such as ammonia and sulphur-rich compounds such as hydrogen sulphide, mercaptans, indoles, and skatole. Indoles and skatole give excrement its most characteristic odour.2 3 The sulphur rich compounds are expecially volatile and can be sensed immediately--this supports the argument that ancestors hid their trail from predators by defaecating into back filled pits.7

Magnetic resonance imaging studies have shown that the anterior insular cortex in the brain is responsible for disgust and is believed to be older than rational thinking.8 The genes for disgust may have arisen by accident and by conferring an advantage through natural selection became common to us all.

Mary Douglas, author of Purity and Danger, believes that aversion to faeces is not inherent nor does it revolve around disease. Instead it is sculpted by society. Nature is carved up in categories. Faeces are ambiguous--is it part of the body or part of the world? The categories are blurred, leading to disgust. Furthermore it is commonly a potent symbol because of its properties of dirt offending against order and therefore threatening to disrupt our stable environment.

All known societies view human excreta as dirty. But different cultures vary; native Indians and African cultures are highly faecophobic, more so than Latin Americans.9 10 Chinese and Japanese cultures are the most faecophilic with a long tradition of using human excreta as fertiliser.11

In Germany, fascination with faeces extends back many centuries with vivid depictions of defecation appearing in medieval paintings and obsessions involving musical and religious figures. Indeed, natural functions were public and exposed in the Middle Ages with people defaecating in the street. Pressure for self control applied over centuries has reduced theseaspects to the private sphere.11

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In Western society, the metaphorical association of shit as a derogatory term has parallels with the way elderly people are valued. Incontinent people with dementia are especially accorded little status or respect--uncontrolled shitting is representative of uncontrolled personhood. Certainly, faeces is not a taboo subject in those working with such people but quite the opposite, arguably a metaphor for the disorder seen in the patients. It is also important in creating positive issues to channel the emotions of the care workers who find themselves in close contact with faeces on a daily basis.11

In India, there is an association between faeces and the untouchables--the lowest of the Hindu caste system that are designated excrement pickers. People are scared of being contaminated by them in the same manner as they are of faeces, which is what the untouchables are seen to have become, particularly to the upper classes.12

Paul Rozin of Pennsylvania University believes that moral and cultural aspects of disgust are clearly learnt, and biological explanations are more likely to have a limited role. His views are more supportive of Freud, who held the opinion that children develop disgust to faeces during toilet training by internalising their parents' attitude to faeces. Rozin has shown that infants under 2 years of age have no aversion to faeces and will actually play with it and eat it. Neonates do not have a disgust response but display distaste in response to bitter or sharp tastes. Until the age of 4 years, children are suspicious but not disgusted, and also do not realise it is potentially contaminating. Children act just like adults by the age of 8, by which time their aversion to faeces is strong. Rozin concluded that disgust is learnt and developed from the inborn sense of distaste.

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Our attitude to faeces is one of the many characteristics distinguishing humans from animals. Unlike us, they have no aversion to faeces, indeed some exhibit coprophagia (eating excrement). Rozin has written, "Anything that reminds us we are animals elicits disgust."

Freud himself holds interesting views on excrement: faeces, penises, and babies "are three solid bodies; they all three, by forcible entry of expulsion, stimulate a membranous passage." He also believed faeces represented past generations, in contrast with that of the present and future associated with babies and penises. The three objects, therefore, demanded special treatment.13 However it was possible for Freud to have stated this arguably through laying emotions aside, including feeling disgust.

In Germany, fascination with faeces was also projected onto the Jews since the Middle Ages. The Judensauer (Jew pig) showing Jews eating its excrement was carved in many places particularly churches of the Lutheran era.14 Luther himself encouraged this, expressing and spreading his hatred for these people. A few centuries later, Hitler painted a new clean vision of German people and compared the Bolsheviks and Jews to contaminants. In Palestine is Still the Issue, Carlton, 2002, John Pilger, the acclaimed journalist, showed how hatred of the Palestinians by the Israeli state manifested itself in desecration of a children's centre with the smearing of shit over walls, equipment, and even the children's paintings. Even in the present time, faeces has been used to express vehement hatred and disgust, most recently as a backlash, after 11 September, against Muslims and targeting mosques.15­17

The smell of human waste is largely despised. Interestingly, humans have a physiological response when exposed to skatole, one of the key chemicals responsible for the stench of faeces. Initially bodily functions decrease, but with continuing exposure, blood pressure and heart rate rise. Stomach convulsions also start, eventually culminating in vomiting. This adverse reaction has inspired the Pentagon's non-lethal weapons programme to develop a stink bomb for crowd control. Using a universally repulsive stench clears the area in seconds.18 But we may be a long way from the time when faeces upholds law and order because of criticism over international arms agreements.

"Faeces as fashion," is the new image for modern art, which has managed to harness aversion to faeces for its own gain. Whether it be Stuart Brisley's (also known as the Curator of Shit) dried and resin injected human faeces, or Cornelius Kolig's alchemy--translating faeces into gold--the aim of such modern art is to disgust yet fascinate the public. These artists see their work as animalistic and passionate, exposing humans for what we really are, especially since they believe that hygiene has cleansed our full self awareness.

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Something else to think about is abnormal behaviour related to faeces. Many pornographic websites deal with coprophilia and coprophagia. However scientific research on abnormal behaviour focuses on animal subjects. Those studies concerning humans have commented on the topics with respect to mental disorders such as schizophrenia, mental retardation, and dementia. Coprophilia in those without such conditions is generally thought of as voyeurism and deviant sexual behaviour and is a frequent source of scatalogical humour.19 At the other end of the spectrum, some people with obsessive compulsive disorders have an overwhelming repulsion for dirt and faeces such that this becomes the focus of their daily routines and lives.

The subject of faeces cannot be simply flushed away. Attitudes to excrement have evolved with time and many reasons and explanations exist as to why aversion to faeces is human instinct for most of us.