Protesters and supporters of the Concerned Student 1950 on the University of Missouri campus. (Jaime Kedrowski/Associated Press)

Trigger warning: If you’re easily disturbed by encroachments on free speech, you should probably stop reading now.

You’ve probably heard about “trigger warnings,” which alert readers or viewers that what lies ahead might be upsetting or offensive. Initially such warnings were intended to help protect sexual assault survivors from reliving their trauma.

But on college campuses, they have lately been demanded for all sorts of other displeasing material.

Among the traumatic topics to which students have objected to being exposed: spiders, “fatphobia,” indigenous artifacts, “images of childbirth,” being told their favorite artist was probably gay, suicide in a ballet, images of dead bodies, nude models in a drawing class, nude images in an art history class and bloody scenes in a horror film class.

Also, the Bible.

These are real subjects of student complaints, as reported by professors in a new survey released by the National Coalition Against Censorship.

About 800 members of the Modern Language Association and the College Art Association, two large scholarship organizations, participated in an opt-in online poll in the spring. While this wasn’t a scientific survey, it nonetheless was the first major attempt to look beyond isolated anecdotes and better gauge the scope and usage of trigger warnings, among other efforts to bowdlerize academic discourse.

The takeaway? Trigger warning mandates remain rare, but plenty of educators (and presumably students) already feel their chilling effects on speech. Eggshells, it seems, lie everywhere, strewn by conservatives and liberals alike.

And if current trends continue, we risk teaching a generation of citizens to care more about avoiding offense than preserving open dialogue, and to flee challenging ideas rather than to rebut or (heaven forbid) embrace them.

Fewer than 1 percent of survey respondents said their institutions had adopted policies on trigger warnings, but 7.5 percent said students at their institutions had initiated efforts to require them. Twice as many — 15 percent — reported that students in their own classes had requested trigger warnings. Likewise, 12 percent said their students had complained when they hadn’t been warned about distressing content.

A majority of educators (58 percent) said they’ve voluntarily provided some sort of warnings about course content, though the warnings may have been broadly worded and they didn’t necessarily allow students to opt out of course materials.

College campuses have created “safe spaces” for all sorts of marginalized groups. But one constituency at Wesleyan University has lost precious real estate, argues The Post's Catherine Rampell. (Tom LeGro/The Washington Post)

Some professors said they thought trigger warnings had pedagogical value. But most expressed anxiety about how they affect academic freedom, and many reported feeling bullied into sanitizing their syllabuses.

Trigger warnings, one educator wrote, force “teachers to change their teaching plans based on calculations about what topics might hurt students’ feelings or make them feel ‘unsafe.’ ”

The report also addressed one common misperception about trigger warnings: that they’re always demanded by lefties.

While media coverage of campus political correctness crusades typically focuses on racial, ethnic and gender sensitivities, professors are getting pushback from conservative and evangelical students, too. (And within the population more broadly, I should note, liberals do not retain exclusive rights to illiberal tendencies.)

Conservative students have objected to classroom discussions of religious beliefs, as well as exposure to sexual or homosexual content. One educator said complaints about the moral propriety of nude models in a studio art class led administrators first to offer trigger warnings and ultimately to stop using nude models altogether.

In another high-profile example, religious students at Duke boycotted the assigned summer reading, “Fun Home,” because the graphic novel depicted nudity and homosexuality.

Such cases, by the way, jibe with other survey data showing that young people are supportive of stifling speech offensive to targets on both the left and right. A recent Pew Research Center survey found that 40 percent of millennials believe the government “should be able to prevent people from saying . . . statements that are offensive to minority groups.” A third of millennials also say the government should be able to prevent speech “offensive to your religion or beliefs.”

In both cases, young people were substantially more likely to express support for such speech limits than older respondents were. In fact, millennials were about four times as likely as their grandparents’ generation to support speech restrictions.

We don’t know whether these discrepancies are mostly driven by aging (maybe today’s 80-year-olds felt the same way in their own salad days) or by cohort (maybe there’s something unusually repressive about this generation of young people). Useful, comparable historical data are hard to come by. At least one survey suggests young people have probably become more allergic to free speech since the 1970s, and anecdotal evidence from professors supports this.

At the very least, our institutions of higher learning are increasingly becoming both victims of, and co-conspirators to, youthful illiberalism.