kernel_task is the core of macOS, so it always shows up in Activity Monitor. When it suddenly takes a large share of the CPU and everything slows down, it’s almost always doing one job: keeping your Mac cool.
Why kernel_task takes CPU
When the processor gets too hot, macOS makes kernel_task occupy CPU time that other apps would otherwise use. The processor does less real work, produces less heat, and cools down. Apple describes this in its support article on kernel_task. The high figure is the symptom; heat is the cause.
That’s also why quitting kernel_task isn’t possible, and why it would be a bad idea if it were.
Common reasons your Mac is running hot
- Sustained heavy work: exporting video, compiling, games, or many browser tabs playing media.
- Blocked airflow: using a laptop on a bed, a sofa or your lap, which covers the vents.
- A warm room or direct sunlight.
- Charging while working hard. On some Intel MacBook Pros, charging from the ports on the left side ran cooler than from the right.
- External displays, particularly high-resolution ones, which add load to the graphics processor.
- Dust in the fans of an older Intel Mac.
How to bring it down
- In Activity Monitor’s CPU tab, find the app doing the heavy work and pause or quit it.
- Put the Mac on a hard, flat surface with the vents clear.
- Try charging from a different port, or unplug a high-resolution display for a while.
- If it happens while the Mac is idle and cool to the touch, restart it. A sensor or process can get stuck, and a restart clears it.
When it’s not heat
If kernel_task is also using a lot of memory, the Mac may be short of memory rather than hot. Check the Memory Pressure graph; the memory pressure guide explains how to read it. Apple silicon Macs run much cooler than Intel ones, so on those, heat throttling is rarer and worth checking first against the other causes of a slow Mac.