Some things are just gross. From oozing, infected wounds to rotting food, there are sights and smells that elicit sheer revulsion.

But disgust isn't just for the delight of middle school boys; it actually serves an important purpose. Researchers have long known that disgust helped our ancestors avoid things that could cause infection. But a new study finds that there are six common categories that trigger disgust and they are based on the people, practices and objects that pose the risk of disease.

For the study, led by the London School of Hygiene & Tropical Medicine, researchers surveyed more than 2,500 people online, listing 75 potentially "disgusting" scenarios they might encounter. The situations ran the gross gamut from people with very obvious signs of infection to objects covered with insects to the sound of sneezing. People were asked to rate their disgust response on a scale ranging from "no disgust" to "extreme disgust."

In not terribly surprising news: Of all the icky scenarios, the one that garnered the most disgust was an infected, pus-filled wound. People who had extremely bad hygiene — such as bad body odor — were also found to be particularly repulsive.

The most disgusting things

Researchers analyzed responses to identify the most common categories of disgust. Here are the categories and some examples, if you have the stomach for them.

  • Poor hygiene — body odor, listening to someone sniffle and snort, an unflushed toilet, watching someone pick their nose
  • Animals — raw chicken, slugs, worms, cockroaches, teeming insects
  • Risky sexual behavior — prostitution, promiscuity
  • Atypical appearance — disfiguration, irregular body shape, illness, poverty
  • Skin conditions — lesions or boils
  • Food that is rotting or spoiled

Each category relates to types of infectious disease threats in our past. For example, the researchers point out that eating rotten food could have led to diseases like cholera, contact with open wounds could have increased the risk of smallpox infections, contact with unhygienic people could have helped transmit leprosy and risky sexual behavior could have increased the chance of an infection such as syphilis.

Our innate disgust response, therefore, keeps us healthy.

The disgust difference

woman holding nose, man's stinky armpit There are some things that disgust women more than men. (Photo: WAYHOME studio/Shutterstock)

The study, which was published in Philosophical Transactions of the Royal Society B, found some gender differences. Perhaps not so surprising, women rated every category more disgusting than men. The researchers point out that this is consistent with knowledge that men, in general, are known to engage in riskier behavior.

“Although we only really came to understand how diseases transmit in the 19th century, it’s clear from these results that people have an intuitive sense of what to avoid in their environment," Micheal de Barra, who co-led the research, said in a statement.

"Our long co-evolution with disease has 'wired in' this intuitive sense of what can cause infection.”

Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science and anything that helps make the world a better place.

Why disgust is good for your health
Researchers find 6 common types of disgust that protect us from disease.