About six weeks ago, Kurt Thorn began feeling a pain in his left arm. It started as a burning sensation in his tendons. Then there was a cyst in his left thumb.

In the lead-up to the US election, the pain got so bad that Thorn, the director of data science at biotech company Zymergen, started wearing a brace on his wrist to prevent himself from bending his thumb in a way that hurt.

The timing wasn't coincidental. His pain was from a repetitive stress injury from holding his phone one-handed and using his thumb to scroll through more and more stories about the election. He was doomscrolling, or compulsively reading bad news on social media feeds or any site with a ceaseless stream of news updates. The term has been in use since at least 2018, but it's become more popular with 2020's surfeit of bad news and our inability to escape the Internet by socialising, attending live events or just going outside.

Thorn, who lives in San Francisco, knew what he was doing but still couldn't stop. "I maybe started doomscrolling more ergonomically," he says. His wife dubs the injury "doomscroller's thumb".

While Thorn's case might be extreme, he is hardly unique in feeling ambivalent about his online news consumption habits, nor in his habit's worsening during the election.

Patrick Dooley estimates he spends several hours doomscrolling every day, even waking up at 3am sometimes to check the news. To get work done during the election, "I had to try to find places that didn't have WiFi," says the artistic director of Berkeley's Shotgun Players.

And though the election is over and there is promising news of a Covid-19 vaccine, doomscrolling is likely here to stay, experts say. If humans sense doom, we will doomscroll.

"We are wired to protect ourselves from danger," says San Francisco psychotherapist Paul Silverman, who treats clients struggling with excessive Internet use. "When we are scrolling through news feeds... and we see this preponderance of Covid and wildfires and violence against people of color and the upcoming election, all of this doom stuff we're scrolling through feels like danger because it is."

He says our brains perceive news as a useful way to prepare for danger, even as that same news makes us more nervous and depressed. "It's raising and lowering the anxiety at the same time," Silverman says.

In Silverman's 16 years of practice, he's noticed that clients' doomscrolling anxieties worsen during elections, adding that the phenomenon has been "pretty pervasive" since 2016. Some clients, he says, are "quite disabled". They open multiple tabs of news sites, scroll through each until they see no new information, then start over at the first one.

"It seems like we're all trying to avoid stress, but the truth is you actually can get addicted to stress," says Dr Anna Lembke, the medical director of addiction medicine at Stanford University School of Medicine, who has a book coming out next year called Dopamine Nation: Finding Balance In The Age Of Indulgence. "You become primed then in this chronic state of fight-or-flight. Then you don't know what to do or who you are when you're not in that state."

The brain releases the hormone dopamine both when you do something pleasurable and, paradoxically, when you're in a frightening situation. Scientists don't know why that is, Lembke says, but a possible explanation is that the body evolved it as a compensatory coping mechanism.

But that only works with danger that ceases at some point, not with a threat that's as endless as a newsfeed. That endlessness means that doomscrolling can still be addictive even if you're a lurker on social media - only reading others' posts as opposed to sharing yourself and seeking the rewards of likes and comments.

Berkeley entrepreneur Aza Raskin invented endless scroll technology in 2006 while working at a small user-interface company called Humanized. He has since expressed regret about how much this now ubiquitous online feature has shaped our lives.

The term doomscrolling, he says, "accurately describes how the technology is used: that it's finding the soft animal underbelly of the human mind and exploiting it." Raskin compares the technology to a wineglass. "If that glass kept refilling invisibly from the bottom, you'd drink much more wine, and that's what infinite scroll does."

Raskin co-founded the Center for Humane Technology in 2013. Asked if endless scroll is humane, he says, "It depends on how it's used and for whose purpose. When I invented the infinite scroll, it was meant as a utility, like a hammer or a saw." Instead of having to click to a next page of search results, say, you could just keep scrolling. "It becomes inhumane when it has a goal of its own, when it wants something from you that's not in your interest."

For social media companies, your undivided, unlimited attention is in their interest, not yours, but they recruit your brain to their side by doling out rewards.

"The reward comes from learning something new about the topic that you didn't know before," says Adam Alter, author of Irresistible: The Rise Of Addictive Technology And The Business Of Keeping Us Hooked and a professor of marketing at New York University's Stern School of Business. "And that reward is unpredictable, which makes it more appealing. The next tweet you read may just hold the piece of information that unlocks the puzzle for you, or changes how you see the issue."

The problem is, he says, "there's no additional control to be gained from consuming your 101st piece of bad news about a topic following your 100th."

There's also a communal element to doomscrolling on social media platforms, one that helps hook even silent lurkers, Alter says. "My hunch is that people would spend less time reading bad news if that news weren't provided by other people."

Some doomscrollers have devised creative ways to moderate their habit. In the spring, New York journalist Karen K. Ho started issuing nightly reminders to her Twitter followers to stop doomscrolling. Sample tweet: "Hi, are you doomscrolling? I understand. There's a lot of worrisome and serious political news, plus really high numbers of Covid-19 cases. You might be tempted to stay up late as an act of agency. How about channeling that into rest, reading a book and going to sleep soon?"

She's amassed 20,000 new followers since she began posting doomscrolling reminders. "They just want something that tells them, with a small level of certainty, 'Go to bed. Or if you can't sleep, here's a tip.' It's pure service journalism, in a way."

Oakland theater artiste and educator AeJay Mitchell, who uses gender-neutral pronouns and calls themself a "reformed doomscroller", works to counter the habit with posts highlighting Black joy and healing. A favourite subject is home-cooked vegan recipes.

"When we're still able to find joy in these places that are so hard for us to exist, that itself is political activism," Mitchel says. "The media loves to show Black grief." Mitchell, by contrast, wants to show the full range of Black experience. "Yes, there's pain. And yes, I just made this deliciously decadent blueberry lemonade pound cake that is fully vegan. That is equally important to me - to the social media landscape - as us screaming about another dead body, us screaming once again about another trans Black woman murdered."

There's also the cold turkey approach. San Francisco playwright and TV screenwriter Christopher Chen deleted all his social media accounts four years ago, when doomscrolling during Trump's election made him feel "down and depressed". He hasn't relapsed since, nor has he been tempted.

He's been working for Amazon TV since March, pitching TV shows, and has been struck by how differently his mind works when it's not distracted by doomscrolling. "This show I'm developing right now came from me thinking in a childlike way, 'What would be my dream show?' I didn't have to listen to anyone. I could just focus on what I would want to see and what would make me happy."

 - TNS