Val Curtis's official title is Director of the Environmental Health Group at the London School of Hygiene and Tropical Medicine, but the first job you'll see in her bio is "Disgustologist." For a new paper published in the Philosophical Transactions of the Royal Society: Biological Sciences, she exposed a group of 2,500 participants to a series of potentially disgusting scenarios and had them rank each by its awfulness. When the hypothetical stench cleared, she was able to classify six distinct triggers sure to make most people want to hurl. Steel yourself — here they are:

1. Bad hygiene. This one is a no-brainer. Seeing somebody fart, pick their nose, or perform other bodily functions in public is stomach-churning, to say the least.

2. Creepy-crawlies. It's not just bugs (but it's definitely bugs). Besides insects, animals like rats ranked high on the yuck list.

3. Scandalous sex. It's hard to say if this one is more social or physiological, but sexual behavior in inappropriate settings was another high-ranking source of disgust.

4. Skin diseases. Besides general bad hygiene, visible skin diseases such as lesions or boils were a particularly potent trigger.

5. Rotten food. Health, hygiene, and insect infestations are all revolting, but there's something about spoiled food that really sets itself apart. Maybe it's all those ... interesting smells.

6. People who aren't doing all that well. What the researchers termed "atypical appearance" included things like a person missing a limb, bearing outward signifiers of homelessness, or with a marginalized body type. Sometimes, disgust arises in pretty unfair ways.

According to Curtis and her co-author Mícheál de Barra, many of these sources of disgust can be tied to a clear source of life-threatening disease and other hazards. Rats, mosquitos, and other tiny terrors can carry deadly illnesses, and rotten-smelling meat won't do your stomach any favors. Similarly, signs of bad hygiene can preface epidemics large and small, unhygienic sex is a great way to catch something awful, and many infectious diseases are transmitted by contact with affected skin.

As for the final category, well, it's certainly not true that an amputated limb is contagious, or that a homeless person is more likely to give you a disease than your coworker who just came back from the bathroom without washing his hands. Sometimes, you need to ask yourself if that feeling of revulsion is coming from a real source of infection, toxin, or harm, or if it's rooted in a social stereotype instead.

It's healthy to listen to your sense of disgust, but it's also good to understand where it's coming from. In other words, you're right to feel revolted by those blue, fuzzy beans in the fridge, but if a person with a disability makes you feel queasy, it might be time to reexamine that reaction.

There's a lot out there that you might not know about — and that you might not want to. But to get to the bottom of the most disgusting facts in the world, you might want to check out "Why Fish Fart: Gross but True Things You'll Wish You Didn't Know" (perfect for grades 4 through 6). We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.