In London on Thursday, the “barbaric” happened: Over about 90 minutes, a pair of teenagers stole a moped, drove around the city and threw acid on strangers. At least five men were injured; one has suffered “life-changing” injuries.

It’s horrifying, and far from an isolated incident. Just a few weeks ago, two Muslims in London were badly burned when a man threw acid through their car window. In April, a 24-year-old went on an acid-attack spree at a nightclub in Hackney, wounding 20. Two people were blinded.

“I don’t want people to think this is happening all over London all the time. It really is not,” Cressida Dick, commissioner of the Metropolitan Police, said after the most recent assault. “But we are concerned, because the numbers appear to be going up.”

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By some measures, Britain has the highest rate of acid attacks per capita in the world. The number of attacks has nearly tripled since 2012, up from 188 to 504. About half of those incidents are classified as “violence against the person.” Another quarter (118) were connected to robberies. So far this year, one person has died from an acid attack and 37 people were gravely injured. (Of course, acid crimes still make up a tiny sliver of crime in Britain. As Rachel Kearton, the National Police Chiefs Council lead for corrosive attacks, told the BBC, the number of acid attacks compared to knife crime is “tiny.”)

Unlike in other countries, men are much more likely to be victims in Britain than women. Experts say that’s because acid attacks are popular among gang members. (Simon Harding, a criminologist at Middlesex University, told the BBC that acid is becoming “a weapon of first choice” for gangs.)

That’s in part because toxic substances such as drain cleaner, oven cleaner or ammonia are much easier to access in Britain than a knife or gun. Corrosive substances “are extremely easy to get hold of. You can buy them from hardware stores and don’t have to register why you’re purchasing it or what you want to use it for,” Harding told USA Today. “If you throw in someone’s face, it’s going to affect their eyes and eyesight so you have a high chance of getting away with it. It’s a very easy thing to do. You can ride up to someone on a bike and throw it at them.”

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It’s also harder to prosecute an acid attack than a knife attack.  ”The charges are more serious if you are caught with a knife and the tariff for prison sentences are much higher,” Harding said. “Acid is likely to attract a ‘[Grievous Bodily Harm] with intent’  charge while using a knife is more likely to lead to the attacker being charged with attempted murder.” He also said that an acid attack can be harder to prove, since there’s rarely any DNA evidence on the scene, and a plastic bottle is much easier to toss than a knife.

To stop the violence, Harding and others recommend making it harder to buy acid and adjusting sentencing to better reflect the severity of the crime. The British government recently began talking to police officers and government officials about banning some acids, a challenge because many are found in common household goods. After this most recent attack, Parliament member Stephen Timms suggested making carrying sulfuric acid without justification illegal, the way carrying a knife is prohibited.

“This is a horrendous crime, it maims, it disfigures,” Kearton explains. “What particularly disgusts me about this crime is that it’s premeditated, no one carries acid around on the streets for any other reason than using it for this reason. … The intention behind this is for someone to live with this for the rest of their lives.”

That’s a reality that Daniel Rotariu, 31, of London, knows too well. A few months ago, Rotariu was blinded in both eyes and suffered burns on a third of his body after his lover threw sulfuric acid on him as he slept. “I have nightmares. … I see it every day, every hour, like it was yesterday,” Rotariu said in his victim-impact statement in court. “More than half of my life I’m gonna have to live it like this. … Sometimes I wish I was dead and I didn’t survive.”