My mother used to say that good manners are like oil in an engine. If you have them, everything runs more smoothly.

But is that all that manners are good for? Valerie Curtis, who might be called the Doyenne of Disgust, writes that manners evolved because we’re so… well, disgusting.

Curtis argues that one of the benefits of being a human is that we’re a very cooperative bunch. By collaborating with each other, we can accomplish great things. But only if we don’t die first. Curtis describes us as a “walking bag of microbes”. My microbes are probably not good for you and vice-versa. So we need to learn to keep our distance.

Curtis writes that manners are fundamental to human nature and evolved from two related systems. The first is the “disgust system, which motivates us to recognise and avoid potential pathogen hot zones.” The second is “the ability to feel shame.” Curtis surmises that feeling “shame if someone looks at us with a disgusted expression” is simply nature’s way of moderating our behavior to keep us from infecting one another.

Manners may have evolved to help us avoid diseases but they also helped us develop complex social systems. Curtis writes, “Humans became adept at looking for clues as to who was likely to cooperate and who was not. Manners provided an indicator. Those who were careful with hygiene were good candidates, as were those who put … the interests of others before themselves.”

While Curtis has a new book out on disgustology, the field has been growing for the past several decades. Other contributors include Daniel Fessler, Jonathan Haidt, Rachel Herz, Daniel Kelly, Paul Rozin, and Joshua Tybur Here are some key discoveries form their work:

It’s not all oral – different researchers proposed different typologies of disgust. Some suggest that there are nine different domains of disgust; others identify only seven. We might immediately identify disgusting smells and tastes. But we’re also disgusted by fleas and immoral behavior.  The world is disgusting in many ways.

Liberals and conservatives view disgust differently – research suggests that liberals and conservatives are similar when it comes to the disgust of disease avoidance and immoral behavior. But conservatives are more disgusted by sexual topics.

Pregnant women are more sensitive to disgust – researchers found that, as progesterone levels increase, so does sensitivity to disgust. This seems particularly true in the first trimester, when the immune system is weakened. Apparently, our bodies protect us from low immunity by increasing our sensitivity to disgust.

It works in advertising — though it hasn’t been studied formally, I can attest that disgust can create powerful advertising and branding campaigns. The Little Lulu illustration above is from a famous campaign that changed our behavior. Prior to Little Lulu’s warning – Don’t Put A Cold In Your Pocket — people often carried cloth handkerchiefs. They sneezed into them and then returned the handkerchief to their pocket. Ewww! If you don’t carry a cloth handkerchief today, you can thank Little Lulu.

Apparently, some of our campaigns have come full circle. Little Lulu changed our handkerchief behavior. Valerie Curtis aims to change out bathroom behavior — and wash our hands more often — with a campaign build around the slogan, Don’t Bring the Toilet With You.  If it works as well as Little Lulu, we could all be cleaner and healthier.

(The Little Lulu ad comes from the Gallery of Graphic Design).