Recently, I’ve been taking note of the instances in which people use “It’s just gross!” as an argument or explanation.

Everyone has a disgust response to some things. When we see, smell or even imagine something gross, we have a physical reaction. Most notably, we make a characteristic face that involves crinkling up our noses and turning down the corners of our mouths. We may also shudder and/or make a “blech” sound. The electric resistance of our skin decreases, which can be measured by a Galvanic Skin Response measurement machine.

Different individuals have different degrees of disgust sensitivity. I’m not that disgust-sensitive. I don’t really notice it if there’s some shmootz on the bathroom floor at times. And I don’t really mind if someone leaves their unwashed macaroni and cheese bowl on the sink counter.

Some people are very disgust-sensitive. I have a friend who really would rather there weren’t any shmootz anywhere ever. And she really can’t stand the thought of used mac-and-cheese bowls hanging out near the sink. When asked why, she simply explains, “It’s gross!” and leaves it at that.

And most people take that as a reasonable response. That is, if you want to argue with her about whether you should be able to leave your mac-and-cheese bowl on the counter with impunity, you’d probably say, “C’mon, it’s not that gross.” But you wouldn’t think to say, “Yeah, it’s gross. But so what?”

We all seem to take the assertion “that’s gross” as a reasonable explanation for why we do things. It seems reasonable that people should act to avoid gross things. But why?

Evolution has endowed us with the disgust response to help us avoid possible pathogen-carrying agents that could get us sick. After all, we tend to have our strongest disgust responses to bodily excretions, decaying food, certain living creatures and things that resemble items in those categories — that is, things that might very well get us sick. So when someone says “that’s gross,” what they might mean is: “That’s dangerous.”

But my disgust-sensitive friend is a pretty healthy person, and this doesn’t seem to change based on whether she’s living with clean or dirty roommates. In fact I could probably convince her that a little floor-shmootz and a few lingering mac-and-cheese bowls won’t significantly increase her probability of getting sick. Yet she still would be grossed out by them and want things to be cleaned up.

Is my friend being unreasonable?

It’s important to remember that having a disgust reaction is unpleasant, and it is (at times) reasonable to act to avoid unpleasant feelings. So when someone says “that’s gross,” what they might be saying in addition to “that’s dangerous,” is: “That’s annoying.” Accordingly, if my friend tells me that my mac-and-cheese bowl is gross, I should wash it because I care about her. That is, she has an unpleasant reaction to seeing the bowl that I seem not to experience. So if I feel bad enough about subjecting her to that, I’ll wash the bowl.

My hunch, though, is that most people who use “that’s gross” to explain their actions or ground arguments intend to be making a different claim from “that’s dangerous” and a stronger claim than “that’s annoying.” I think they intend to be saying something more like “that is an unacceptable state for the world to exist in.” Or, put simply, “that’s wrong.”

It seems that people tend to use their disgust response as an indicator that a moral violation has occurred. At times, the disgust reaction has been used to justify bans on gay marriage (“gay sex is gross and therefore wrong”). It has been used to justify genocide (“those people are gross and therefore bad”).

These are extreme examples, but I come across arguments like these all the time: My mom thinks it’s wrong to wear a pair of pants and then return them because it’s gross. My sister thinks soap shouldn’t be made with animal fat because it’s gross. Perhaps returning worn pants and making soap with animal products are wrong. But not because they’re gross.

The disgust reaction is a tool we should use to help us steer clear of danger in the environment. It’s also something we should keep in mind to avoid annoying our roommates. But we need to be vigilant about moral arguments that are founded on the mere intuition that “that’s gross.” Such arguments can be deeply dangerous — not to mention annoying.