Why a Mac slows down when it gets warm

27 October 2026 · 6 min read

A Mac slows down when it gets warm because it deliberately lowers the speed of its processor to keep the temperature safe. This is called thermal throttling, and it is a protection, not a fault. Less speed means less heat, so the Mac trades performance for safety until it cools down. The fix is to remove the heat source: find what is working hard, let the Mac breathe, and take the load off.

What is happening

A processor makes more heat the harder it works. Your Mac has a way to get rid of that heat: a heatsink, a fan in most models, and the airflow through the case. When the work being done makes heat faster than the Mac can get rid of it, the temperature rises. Before it reaches a harmful level, the Mac lowers how fast the processor runs. The Mac gets slower, makes less heat, and the temperature settles.

You do not turn this on or off, and you cannot tune it with a setting. It happens automatically, and it undoes itself when the Mac cools.

On a MacBook with no fan, or a fan that cannot move enough air, this happens sooner under steady heavy work, because the case itself is doing the cooling. A desktop Mac has more room to move heat, but it can still be limited by blocked vents or a warm room.

How it looks from the outside

You will not get a message. These are the signs:

The Mac was fast and gets slower after a few minutes of heavy work, such as an export, a game or a long video call.
The case, usually above the keyboard on a laptop, feels warm or hot.
The fans, if the Mac has them, speed up and get loud. What to do when your Mac fans get loud is the place to start for that.
Frame rates drop, or an export that started quickly becomes slower, though you changed nothing.
It recovers when you stop for a while.

Slowing down at the same point every time, such as always about ten minutes into the same task, is a good clue that it is heat and not a software fault.

A place to see it: kernel_task

There is one place the slowing-down shows up in a list of processes. A process called kernel_task is the core of macOS. When the Mac is limiting the processor to stay cool, kernel_task can show high CPU use, because it takes up processor time that apps would otherwise get. That sounds backwards, but it is how the Mac holds apps back.

In Foreman, kernel_task shows with a plain-English name, “macOS kernel”, and Foreman describes it this way: the core of macOS, where high CPU often means the Mac is slowing itself down to stay cool. There is also a process Foreman calls “Temperature monitor” (thermalmonitord), which watches temperatures and slows the Mac down when it gets hot.

Two cautions. First, do not try to end either of them: the slowing is protecting the Mac, and Foreman never offers to end kernel_task. Second, a high kernel_task figure points at heat, but it does not prove it, because other things can also affect it. Use it as a clue next to how the Mac feels. What is kernel_task on a Mac and why does it use so much CPU explains it in more depth.

Foreman does not show temperatures or fan speeds, so it cannot tell you how hot the Mac is. What it can show is the thing that matters for the fix: which app is making the Mac work.

What makes a Mac warm

Heat comes from work, and from anything that stops heat leaving.

Sustained work. Exporting video, playing games, compiling code, running a virtual machine, a long video call and heavy photo or music processing all keep the processor and graphics busy for a long time. Short bursts rarely cause throttling. Long runs do.

A background app that is stuck. Something using a lot of processor time with nothing to show for it. This is the most useful one to find, because it is heat for no benefit.

Blocked airflow. Using a laptop on a bed, a sofa or a blanket covers the vents and traps heat. So does a case or stand with no gap under the Mac. A hard, flat surface, or a stand that lifts the Mac, helps.

A warm room or direct sun. The Mac cools by passing heat to the air, so warm air takes less heat away.

Charging while working hard. A laptop charging and under load has more heat to deal with than one that is only doing one of those.

Dust. On older Macs with fans, dust inside can reduce cooling. Cleaning inside is a job for a repair shop if you are not sure how.

Find the app that is making the heat

Open Foreman with Control-Shift-Escape (⌃⇧⎋) and go to Processes.
Click the CPU column to sort. The app at the top is doing the most processor work. Open its row to see its helpers.
Check GPU too, by clicking that header, because games, video and browsers heat the Mac through graphics as well as the processor.
Ask whether the top app deserves to be there. If it is the export you started, it is doing what you asked. If it is something you are not using, it is a problem to fix.

For an app you do not need, End Task asks it to quit normally. For one you want open but not right now, Efficiency Mode holds it to about a quarter of the processor time it would take while it is in the background, which means less work and less heat from it. In front, or while playing sound, the app runs at full speed. Do not expect a particular drop in temperature, because how much it helps depends on what else the Mac is doing.

If the app at the top is a browser, open its row and look for a single heavy tab. Why your MacBook gets hot and how to find what’s heating it has more on tracking down the cause.

Simple things that help, with no app at all

Put the Mac on a hard, flat surface, or on a stand that lets air under it.
Keep the vents clear, and do not cover the keyboard area with anything.
Move out of direct sun and away from heat sources.
Close what you are not using before a long task.
Take a break in a long task. A few minutes can let the Mac cool and speed up again.
On many MacBooks, System Settings > Battery has a Low Power Mode. It trades some speed for lower energy use, which can also mean less heat and quieter fans.

When it is not heat

Not every slowdown is thermal. If the Mac is slow while the case is cool and the fans are quiet, look at memory and disk instead. Why is my Mac so slow: how to find the app to blame is the general method.

Foreman is free for 24 hours and then $12 once, and works on up to 3 Macs running macOS 14 Sonoma or later.