What's in Bear Spray?

Fire off a can of bear spray and you’ll deploy a 25-foot-long hot pepper cloud that should prevent a bear from attacking. The stuff’s not lethal, but it will temporarily irritate a bear’s eyes and lungs enough that the animal will likely move on. You don’t spray it onto your body like, say, Deep Woods Off. (More on that in a bit.)

The stuff works. Professors Tom Smith and Steve Herrero have studied hundreds of bear attacks in Alaska and found that 93 percent of the time it was used, the bears ceased their aggression or activities like rummaging through trash. Bears injured only 2 percent of the people who deployed bear spray, compared to 56 percent of the people who tried to fend them off with a gun.

So, what’s in the can, and how does it work?

It starts with pepper, usually oleoresin of capsicum—a waxlike extract of hot peppers. Most manufacturers, says Smith, use the same stuff found in nearly every nonboutique brand of spicy food, from Tabasco to Hormel chili. Undiluted, it ranks on the Scoville heat unit scale at 3.2 million to 3.6 million. For reference, habanero peppers hit between 80,000 to 200,000. Because capsicum is so potent, the EPA, which regulates the sprays, says bear spray cannot contain more than 2 percent of the stuff.

Because it’s oil-based, capsicum is also sticky and tenacious. “If it’s discharged in a campground, the area is dead to the world for 24 hours,” says George Hyde, general manager of Counter Assault, the oldest manufacturer of bear spray. “Walk across the ground and it’ll become reatomized. Spray it on your tent or clothing and you’ll probably never use those things again.” Don’t think about it like the bear-repellant equivalent of DEET. “It happens every summer,” says Hyde.

Then there’s the carrier, which holds the capsicum in an evenly mixed liquid state so you don’t have to shake the can before use. These vary between manufacturer and are typically trade secrets, but they make up 8 eight percent of the spray.

Finally, there’s the propellant. Almost every manufacturer uses R134a—the same gas used as a propellant in asthma inhalers. The chemical actually boils when it leaves the can, atomizing the chemicals mixed with the propellant into a cloud. Bear spray is pressurized to 80 pounds per square inch, making it capable of firing the mixture out of the nozzle at 75 miles per hour.

That propellant is the reason bear spray canisters have a four-year expiration date. No matter how good the seal between the can and the plastic nozzle, the cans lose pressure over time. It’s also why bear spray canisters can explode if left in a hot car. In one instance, says Hyde, someone left their can on the dashboard. When it exploded, the windshield was left with an orange-rimmed, six-inch-wide hole. The lesson: If you leave your bear spray in the car, throw it in a cooler. Even one without ice should keep the canister below explosive temperatures (somewhere around 180 degrees Fahrenheit for many cans). Conversely, the bear spray will work at temperatures below freezing, Smith says.

So what happens when you push the trigger and these three ingredients hit the air? When capsicum hits the bear’s face, the animal’s eyes close, its lungs constrict, and its body starts producing as much mucus as possible to expel the pepper. The bear is crying, wheezing, and coughing. “The bear goes from fight directly to flight,” says Hyde. “In one account, the bear turned to run from the spray and ran right into a tree.”

Bear spray works just as well on other animals. “If it has eyes and lungs, people have sprayed it with bear spray,” says Hyde. The list includes mountain lions, dogs, wild pigs, and moose. Hyde reports there are more instances of the spray being used on moose, which can be quite aggressive, than on bears. There is at least one case of Counter Assault being successfully used on a rattlesnake.

Of course, pepper spray is also used on people. Counter Assault and its main competitor, UDAP, both make pepper sprays for law enforcement and self-defense purposes. Police recently used it on protesters in Baltimore and Ferguson, Missouri. The difference between the products is the percentage of capsicum. The FDA has ruled that pepper spray used on people can contain no more than 1.3 percent of the pepper mix. The spray pattern is also different—law enforcement uses a more concentrated spray pattern so it gets on fewer people.

There’s some debate about how to best use pepper spray on bears. Some people say you should be upwind of the bear so the spray blows onto the bear. Others suggest shooting low, even bouncing the spray off the ground so it is assured of hitting the bear’s mucous membranes. Smith says those ideas are great in theory, but in practice, when faced with a charging bear, it’s best to just go ahead and use the spray no matter the conditions. “If you get too cute with it, you might end up mauled,” he says.

A big reason bear spray works as well as it does, according to Smith: it gives you a reason not to flee. “If you turn and run, you are as good as attacked,” he says. “When you are being charged by a bear, it’s really difficult not to turn and run. Focusing on using that can of bear spray is often enough to make you stand your ground, which usually deters the attack.”