Doomscrolling names the behaviour — compulsively reading bad news. Brainrot names the content and its alleged effect. You can brainrot on entirely cheerful slop.
Side by side
Aspect
Brainrot
Doomscrolling
Names
The content and its effect
The behaviour
Requires bad news
No
Yes
Coined
1854
2010s
Clinical status
None
None
What each one means
Brainrot
Low-quality, hyper-stimulating online content — and the mental dulling blamed on consuming too much of it. In fandom it also means obsessive fixation on a piece of media. Older and broader: the decay of mental faculties, intelligence or moral character from any cause — Thoreau used brain-rot that way in 1854.
Doomscrolling is the compulsive habit of scrolling through a bottomless feed of bad news, unable to stop even though it keeps making you feel worse. The feed never ends, so neither does the search for one more thing to dread.