Valerie Curtis is fascinated by feces. And by vomit, pus, urine, maggots and putrid flesh. It is not the oozing, reeking substances themselves that play on her mind, but our response to them and what it can teach us.

The doctor of anthropology and expert on hygiene and behavior says disgust governs our lives - dictating what we eat, wear, buy, and even how we vote and who we desire.

In science, disgust has languished unstudied - it was once dubbed the "forgotten emotion of psychiatry" - while emotions like fear, love and anger took the limelight.

But Curtis, who refers to herself half-jokingly as a "disgustologist", is among a growing group of scientists seeking to change that by establishing the importance of the science of revulsion in everything from sex and society to survival.

"People are disgusted by things without even realizing it. It influences our lives in so many subtle ways, and it's really important that we understand how great that influence is," she told Reuters in an interview.

Parasite avoidance theory

Curtis's somewhat revolting interests stem from her many years of work in public health, seeking to improve hygiene and reduce unnecessary death and disease around the world.

As a director at the internationally respected London School of Hygiene and Tropical Medicine, she has conducted research into hygiene behavior in Bangladesh, Burkina Faso, China, India, Uganda, Vietnam, Indonesia and Kyrgyzstan.

In 2002, she founded a global public-private partnership involving the U.N. children's fund UNICEF, the World Bank and the household product multinational Procter & Gamble to promote hand-washing.

"I've been trying to understand disgust for 30 years, and what I've found is that people the world over are all disgusted by similar things: body products, food that has gone off, sexual fluids - which, with a few exceptions, we don't tend share with other people - bad manners and immoral behavior," she said.

In a book to be published this month entitled "Don't Look, Don't Touch", Curtis argues that while revulsion at rape and disgust of dog poo seem at first glance to be very different things, they have common roots in what she calls a "parasite avoidance theory" of disgust, or PAT for short.

It looks at disgust from an evolutionary perspective, arguing that our most repulsed ancestors were aided in the "survival of the fittest" race by their disgust instinct - avoiding disease, deformity and death - and thereby living longer, having more relationships and producing offspring with a sense of "healthy squeamishness".

Curtis compares the disgust response with fear and its flight or fight response - which makes us instinctively run away from or avoid things that might eat us.

"Even more importantly for our evolution was disease," she said. "Disease is something that will eat us up from inside - and what's important is that disgust keeps you away from them.

"Disgust is an organ - like an eye or an ear. It has a purpose, it's there for a reason," she said. "Just like a leg gets you from A to B, disgust tells you which things you are safe to pick up and which things you shouldn't touch."

Microbes to morality

Avoiding dirt and disease also requires us to avoid each other, to a certain extent, Curtis says, which is how disgust also drives manners and socially acceptable behaviour.

"Every time we come into contact with other people we do a sort of disgust dance - where we want to get close to people and have social interaction with them, but at the same time we are also terribly careful not to disgust them."

And so, she argues, evolved manners and social behaviour.

"With disgust, you start with microbes, go on to manners and then on to morality," she says. "It's an emotion that teaches you how to behave. It helps build the moral framework of society."

It's this all-encompassing reach, according to Curtis, that makes disgust so fascinating - and that has brought it in from the cold as far as serious academic research is concerned.

While 10 years ago, there were probably fewer than a handful of research papers on disgust or revulsion published in scientific journals, now there is a vast scientific literature and many books dedicated to picking them apart.

"It's actually now become a bit of a plaything of scientists," says Curtis.

In the lab, she adds, where scientists seek to observe and analyse causes and effects of human emotions, it is difficult and dangerous to generate real fear, and nigh on impossible to induce genuine love, but disgust is far easier to create.

"Disgust is fascinating because it's a model emotion," she said. "It tells us a lot about how all the emotions work."