Phone getting hot for no reason? Here's how to find out why

Some warmth is genuinely normal charging, navigation with GPS running, or a long video call will all warm a phone up a bit, and that's not a problem. What's worth investigating is heat with no obvious cause, especially while the phone is just sitting idle.

Check what's actually using the CPU

Same screen as the battery drain guide: Settings → Battery on iPhone, or Settings → Battery → Battery usage on Android. An app using unusually high battery while you weren't actively using it is almost always also the source of unexpected heat the two go together, since heat is mostly a byproduct of the processor working hard.

A stuck app in the background, not actually closed

Sometimes an app you "closed" is actually still running a process in the background a map app that didn't fully release GPS, a video call app that didn't release the camera properly. Force-closing it fully (swiping it away from the recent apps screen, not just leaving the app) often resolves heat that built up from this specific kind of stuck process.

Direct sunlight is a bigger factor than people think

Leaving a phone on a car dashboard, a windowsill, or anywhere in direct sun for even 10-15 minutes can heat it up significantly, sometimes enough to trigger a temperature warning. This isn't a software problem at all and the fix is simply moving it to shade but worth ruling out before assuming something's wrong internally.

Charging with a case on

Certain phone cases, especially thicker or rugged ones, trap heat that would normally dissipate during charging. If your phone runs warm specifically while charging, try removing the case for that one session as a test. I've seen this make a noticeable difference on phones with otherwise normal charging behavior.

A bad battery can cause heat, not just drain

Same battery health check as before applies here: Settings → Battery → Battery Health on iPhone. A degraded battery doesn't just lose capacity, it can also generate more heat than a healthy one during normal use. If heat is paired with noticeably worse battery life too, this connects the two symptoms to one underlying cause.

What it was for me

A maps app that hadn't released GPS properly after I closed it exactly the stuck background process described above. Force-closing it from the recent apps screen and not just backing out of it fixed the warmth within a few minutes.