Known as nonlethal or less-lethal weapons, many of these tactics were originally pitched as a way to make warfare more humane by incapacitating a person or encouraging them to flee. Law enforcement agencies later adopted these weapons from the military as an alternative to using firearms.

Yet people who study nonlethal weapons wonder if a reclassification is in order, as research continues to reveal their damaging ramifications on the body. When misused, these weapons break bones, burn the skin, and cause internal injuries that can be fatal. Here’s a look at when and why serious injuries occur with nonlethal weapons, and what people can do to protect themselves.

Tear gas is uniquely designed to make its victims miserable.

When a canister of tear gas is fired and detonates, it releases a cloud that engulfs anyone nearby. Chemicals in the gas sting their eyes, skin, and even their airways, and excruciating pain pulses throughout the body. They cough, sneeze, and form so much mucus it can feel like being suffocated. Ultimately, they’re forced to run away.

This response is exactly why law enforcement officers around the world use tear gas as a riot control method, says Sven Eric Jordt, associate professor of anesthesiology, pharmacology, and cancer biology at the Duke University School of Medicine.

The active agent in tear gas is an organic compound called CS, named after the two American chemists—Ben Corson and Roger Stoughton—who identified it in 1928. Jordt was a member of the research team that discovered CS binds to a pain receptor in our nerves named TRPA1. This pain sensor is located all over the body—eyes, skin, lungs, mouth—and is responsible for the zesty sensation triggered while eating wasabi or horseradish.

These chemical irritants are considered nonlethal in open environments and at low concentrations. But in large doses—administered when they detonate next to someone or in a confined space—the chemicals can kill tissue in the airway and digestive system, fill the lungs with excess fluid, and cause internal bleeding. Jordt says this is why it’s important to flush it out with water immediately to decontaminate, and to get rid of contaminated clothing as well. He doesn’t recommend using milk, as some protesters have done, since it is not sterile and could lead to infections and further irritation. When the body senses such a noxious presence, its defenses jolt to action.

“The nose basically acts as a kind of sentinel for inhaled threats, to signal alarm if there’s anything around that might injure the lung,” Jordt explains. The sensory motor system responds with involuntary reflexes that are normally used to expel unwanted pathogens, including coughing, sneezing, crying, and excess mucus production. This response can be dangerous for someone with underlying conditions such as asthma or arrhythmia. Physicians for Human Rights has also suggested a possible link between tear gas and miscarriages, though the connection remains understudied and based on anecdotal evidence.

Pepper spray, based on a compound called oleoresin capsicum (OC) that can also be used in grenades, behaves in a similar way. It is extracted from extremely pungent chile peppers and activates many of the same pain fibers as CS, though via a different nerve receptor. Pepper spray is not as chemically reactive as tear gas—meaning its use is less likely to result in severe chemical burns—but it causes the same debilitating reflex responses that can be especially harmful to people with underlying conditions.

While they may be classified as nonlethal, Jordt says all these weapons are far from harmless.

“We also have to acknowledge the police are sometimes not using this properly,” Jordt says. Tear gas is intended to be deployed at a distance. When canisters are launched directly at crowds, they’re prone to causing serious eye, head, brain, or chest injuries from the force of impact, as well as the chemical burns.

Emerging evidence suggests that tear gas exposure can have long-term consequences for the respiratory system. In 2014, for example, a study into the use of tear gas in military training linked CS exposure to the onset of acute respiratory illnesses. The long-term effects on civilian populations are unknown, and these groups are far more likely than young military recruits to have underlying health conditions.

In 1970, the British army introduced rubber bullets as a tool to control riots in Northern Ireland. Made of rubber—and, in some cases, rubber-coated steel—these projectiles were designed to be less lethal than metal bullets. Their larger surface areas slow their pace during flight, allowing them to administer blunt force to the body, rather than penetrate it.

Jennifer Stankus, a clinical faculty physician at the Madigan Army Medical Center Department of Emergency Medicine, likens it to getting shot with a paintball gun. Yet serious injuries from rubber bullets have been reported throughout their history. Studies of their use in the conflict in Kashmir have shown that rubber bullets can cause fractures, nerve and tendon injuries, and infections. Other studies indicate that rubber bullets can cause internal organ damage leading to death or permanent disability. This week, a Sacramento teen was hit in the face with a rubber bullet that broke his jaw and left a gash across his cheek.

The United Nations Human Rights Guidance on Less-Lethal Weapons in Law Enforcement recommends only using rubber bullets when facing imminent threats—and aiming at the lower abdomen or legs, where they are more likely to cause bruises and lacerations. Stankus says that’s the most common scenario, and that more serious damage generally occurs only when these weapons are fired at close range.

But when shot at close range, rubber bullets cause damage on par with a car accident. The blunt force can break bones and crush or tear the blood vessels in the area of impact—which can cause bleeding in nearby organs, such as the kidneys, spleen, or liver.

Normally, those internal injuries can heal themselves. But in some cases—such as among those with underlying conditions—blood can fill the organ or spill out into the abdominal cavity. Worse, Stankus says, is the possibility of getting hit in the eye, taking a rubber bullet to the skull, or spinal cord injuries. This is why protesters have taken to wearing helmets and goggles, and covering their skin.

Stankus says that severe injuries from rubber bullets are rare overall, and she doesn’t dispute their nonlethal classification. But organizations like the Physicians for Human Rights disagree, arguing such incidents have occurred frequently enough that rubber bullets should be prohibited as a tool for crowd dispersal.

Military helicopters hovered low over protesters in Washington, D.C., on Monday night, sending debris flying and leaving people covering their ears. Meanwhile, police forces across the country—including Seattle, Houston, Portland, and Denver—exploded flash-bangs, so called for the way they emit a loud bang and bright lights as they detonate.

Noise is a common tactic for clearing people out of an area, says Richard Neitzel, an associate professor at the University of Michigan School of Public Health who studies the effects of noise exposure. Aside from being irritating, noise can harm the body in two ways, both of which target the inner ear.

Prolonged exposure to noise can also wear down those hair cells, like trampling on blades of grass. “If you walk across a lawn once a year, those grass blades are going to spring back up,” Neitzel says. “If you’ve got a troop of soldiers marching back and forth across this lawn constantly, you’re going to end up damaging those blades of grass such that they don’t recover.”

The ear can handle loud noise to an extent. Determining whether tactics like low-flying helicopters or flash-bangs cause acoustic trauma relies on three factors: the intensity of the pressure, how long someone is exposed to it, and how often the pressure occurs.

Hovering helicopters might be as loud as an outdoor concert—95 decibels—enough to cause damage after about 50 minutes. But Neitzel says a few minutes’ exposure brings no real risk of hearing loss. More concerning, he says, are the potential effects of flash-bang grenades. These emit sounds upward of 170 decibels, which can cause immediate ear injury to anyone standing nearby—a risk that increases with the number of explosions. Neitzel also points out that anyone living in a city with helicopters constantly circling overhead may suffer consequences from prolonged noise exposure. He notes, though, that ear plugs will help mitigate some of these effects.

Stun guns have been a method of quelling—and inciting—unrest since the 1960s, when law enforcement used rudimentary versions of the devices on civil rights activists. These guns deliver short blasts of electric current to the body and are designed to subdue assailants just long enough to restrain them. But they, too, can be lethal.

These weapons shoot two barbed darts sharp enough to penetrate the clothes and skin and embed themselves into the body’s tissue. The darts connect to very fine wire that transmits five-second blasts of energy. To complete a circuit, the electricity travels from one dart to the other through body tissue. As it does so, it stimulates the skeletal muscles to twitch so fast, it’s like having a seizure.

If the darts hit the wrong parts of the body, these weapons can cause cardiac arrest, according to a 2014 article in the journal Circulation.

That’s because stun guns can mess with the heart’s finely tuned pumping, says Douglas P. Zipes, author of that study and distinguished professor emeritus at the Indiana University School of Medicine. Hearts beat when the sinus node, a small mass of tissue in the right upper chamber, transmits an impulse to the heart cells. If the heart happens to be in the path of the current traveling from dart to dart, the electricity can accelerate that process—ultimately revving up the heart rate to unsustainable levels. If a police officer overrides the safety on a stun gun to transmit electricity for longer than five seconds, it could cause brain injury or death.

Other parts of the body are also vulnerable. Scientists have recorded a handful of cases of spinal fracture, which they theorize were caused by the sudden severe muscle contractions. A 2016 study showed that Tasers can impair short-term cognitive function. A dart can also inadvertently puncture the eye.

To protect against these potential outcomes, Zipes says, law enforcement officers should avoid shooting toward the chest and overriding the safety on their stun guns. They also need to recognize that these weapons can cause cardiac arrest so that they can begin resuscitation immediately if someone they’ve shot becomes unresponsive.

Zipes says this is why context is so important when discussing the lethality of so-called nonlethal or less-lethal weapons. “A club might be called a nonlethal weapon used by law enforcement for defense,” he says. “But obviously if you sledge somebody over the head with it hard enough, it’s going to kill.”