Some women carry it in their purses, in a pink, lipstick-shaped container. Hikers use it to deter bears. People in most states can buy a small canister of it on a quick-release key ring on Amazon.com for $7.07.

As pepper spray has become ubiquitous in this country over the last two decades, it has not raised many eyebrows. But now, after images of campus police at the University of California, Davis, spraying the Kool-Aid-colored orange compound on docile protesters on Friday, pepper spray is a topic of national debate.

It has become the crowd-control measure of choice lately by police departments from New York to Denver to Portland as they counter protests by the Occupy Wall Street movement.

To some, pepper spray is a mild, temporary irritant and its use has been justified as cities and universities have sought to regain control of their streets, parks and campuses. After the video at Davis went viral, Megyn Kelly on Fox News dismissed pepper spray as “a food product, essentially.”

To the American Civil Liberties Union, its use as a crowd-control device, particularly when those crowds are nonthreatening, is an excessive and unconstitutional use of force and violates the right to peaceably assemble.

Some of the students at UC Davis are threatening civil suits against the university on these grounds. The chancellor has called the use of pepper spray “unacceptable” and has put the officers on administrative leave.

“The courts have made it very clear that these type of devices can’t be used indiscriminately and should be used only when the target poses a physical threat to someone,” said Michael Risher, staff attorney for the ACLU of Northern California.

To Kamran Loghman, who helped develop pepper spray into a weapons-grade material with the FBI in the 1980s, the incident at Davis violated his original intent.

“I have never seen such an inappropriate and improper use of chemical agents,” Loghman said in an interview.

Loghman, who also helped develop guidelines for police departments using the spray, said that use-of-force manuals generally advise that pepper spray is appropriate only if a person is physically threatening a police officer or another person.

In New York, for example, a police commander who sprayed several women in an Occupy demonstration last month faced disciplinary proceedings. The New York Police Department says pepper spray should be used chiefly to control suspects who are resisting arrest or for self-defense.

To many watching from the sidelines, pepper spray remains an obscure agent, even as the video of its spraying at Davis has become the defining image of an otherwise amorphous Occupy movement.

Pepper spray — its formal name is oleoresin capsicum, or OC spray — finds its power in an inflammatory agent that occurs naturally in more than 300 varieties of peppers, including cayenne, and that vary by their degree of hotness. (Black pepper is not part of the capsicum family.) When sprayed in someone’s face, it causes an intense burning sensation of the eyes, resulting in temporary blindness, while it also restricts breathing, induces coughing and leaves the person at least temporarily incapacitated.

Pepper’s use as a deterrent dates to the ancient cultures, in China and India, which sometimes used it in war, sometimes for torture. Because it was effective, cheap and widely cultivated, pepper persisted as a weapon through the ages, mostly for self-defense. Some Japanese women kept it tucked into their kimonos in case a man made aggressive advances.

It is now used the world over in its spray form, under numerous brand names, mostly to foil criminal suspects but also for self-protection against both humans and animals.

But the public rarely witnesses such scenes, and that was one of the reasons that the video from Davis was so powerful. It captured many elements — seated protesters being doused with a bright orange spray by campus police, whose body language appeared surprisingly casual.

“What makes this so oddly interesting is that those officers don’t look like the Chicago police in 1968,” said Robert Thompson, a professor of popular culture at Syracuse University. They are so casual, he said, “it’s as if they were called because someone was sunbathing naked on the quad.”