When you install an Android update, your phone does not simply swap out some files and carry on. It has to recompile the code for every app you have installed so that each one runs properly on the new system version, a job Android handles through a process called dex2oat, and on a phone with sixty or seventy apps that is genuinely heavy work. This is why the heat shows up even when the phone is sitting on the table doing nothing you asked it to do. The processor is busy, and a busy processor is a warm one.
Most of the panic around this comes from not knowing that the work is happening at all, since the phone finishes its visible “optimising apps” screen and then quietly keeps going in the background for days. That said, not every case is harmless, and there is one specific sign that means you should stop using the phone rather than wait it out. We’ll cover what your phone is actually doing after an update, how long it should reasonably take, the difference between normal warmth and a real problem, and what to do in each case.
Your phone rebuilds itself after an update, and that is where the heat comes from
The recompiling is only the first item on a fairly long list. Once that finishes, your phone re-indexes storage so search and the gallery work again, rebuilds thumbnail caches for every photo and video you own, and re-establishes the background services that handle sync and notifications. Google Photos often decides to re-verify your backup at the same time, which on a Nigerian data connection means hours of upload activity keeping both the processor and the radio awake. Samsung phones do their own additional pass on top of all this.
The Play Store adds another layer that people rarely connect to the heat. A system update usually triggers a wave of app updates, so while your phone is already busy recompiling, it is also downloading and installing twenty or thirty apps, each of which then needs compiling itself. Everything in that list is one-off work rather than a permanent change, which is the main reason this settles by itself. It is worth knowing that Android schedules much of this work for when the phone is charging and idle, so a phone left on charge overnight will get through it faster than one you keep picking up.
How long is reasonable, and why an older phone takes longer
Two to three days of noticeably warmer running is normal, and up to about a week is still within the range you would expect on an older or heavily loaded device. A phone with 4GB of RAM and an entry-level chip has to do exactly the same amount of compiling as a flagship, just more slowly, which stretches the same workload across more days. If your storage is nearly full it takes longer again, because the system needs working space to write the compiled output and spends time shuffling data around to find it.
Ambient temperature is the part that never gets mentioned in guides written elsewhere, and it matters a great deal here. A phone doing background work in a 20 degree room and the same phone doing the same work in Lagos in March are two very different situations, because the device sheds heat into the air around it and warm air carries less of it away. Add a thick protective case and a spell of using the phone outdoors, and a device that would have felt mildly warm somewhere cooler feels alarming here. The workload has not changed, only the conditions it is running in.
Heat also arrives alongside two other complaints for the same underlying reason, which is why so many people report all three together after an update. The battery drains faster because the processor is working, and the phone feels sluggish because that work competes with whatever you are trying to do. We covered those separately in what happens when your battery gets worse after an update and why your Android phone gets slow after updates, and photos can shift too, which is the subject of why camera quality changes after a software update.
A swelling battery is not a wait-and-see problem
Everything above is about heat that resolves itself. This one does not, and it is worth separating from the rest because the response is completely different. If the back cover of your phone is lifting away from the frame, the screen is bulging or sitting proud of the body, the phone rocks when placed flat on a table, or the case no longer fits properly, the battery is swelling. That is a lithium cell venting gas, and it is a fire risk rather than a performance complaint.
Stop charging it, power the phone down, and take it to a repair technician for battery replacement. Do not press on the bulge, do not try to prise the battery out yourself, and never puncture it, because a punctured lithium cell can ignite. Keep it away from your bed and off soft furniture until you can get it seen to. An update did not cause this, though the extra load from post-update work can make an already degraded battery show symptoms that were building up anyway.
The other signs that point to a fault rather than a busy phone
Short of a swollen battery, a few patterns mark out a genuine problem. Heat that is still there after two weeks has outlasted anything background optimisation can explain. A phone too hot to hold comfortably against your ear, or one that shows a temperature warning and shuts itself down, has gone past the range manufacturers design for. Heat concentrated in one specific spot, particularly around the charging port, points at hardware rather than software. And a phone that runs hot while genuinely idle, with the screen off and nothing scheduled, after that first week has passed is not doing normal work.
The battery usage screen settles most arguments here. Go to Settings > Battery > Battery usage and look at what is at the top of the list. Android System or Android OS sitting high is exactly what post-update optimisation looks like and is reassuring rather than worrying. A single third-party app dominating the list means that app is the problem, and it can be dealt with directly, which is what we did in the guide to WhatsApp battery drain. Checking whether other owners of your exact model reported the same thing after the same update version is the other quick test, since a wave of identical complaints in the same week means a software defect and a patch will usually follow.
What actually helps while the phone works through it
The most effective thing you can do is give the phone a clear run at the job. Leave it on charge overnight with the screen off and let the scheduled optimisation finish rather than interrupting it repeatedly, and take the case off while it does. Beyond that:
- Restart the phone once, which clears any process that got stuck partway through the update.
- Let the Play Store finish updating everything in one go instead of leaving it to trickle through over a week.
- Free up storage if you are close to full, since compilation needs somewhere to write. Our guide to storage that keeps filling up covers where the space usually goes.
- Avoid gaming or long video calls while charging, because charging generates its own heat and stacking the two is what pushes a phone into throttling.
- Keep it out of direct sun and off the dashboard of a parked car, which will heat a phone far beyond anything an update can.
Skip the booster and cleaner apps entirely. They sit in memory permanently and force close apps that Android was deliberately holding in a cached state, which means those apps then have to be reloaded from scratch, generating more work and more heat than they saved. Putting the phone in the fridge or freezer is worse still, since condensation inside a warm device is how you turn a temporary heat problem into permanent water damage. If you want to reduce the load generally, the ways to boost Android battery life without installing anything apply here too, because less background activity means less heat.
A factory reset is worth considering only after two weeks of no improvement, and only when other owners of your model are not reporting the same fault, since wiping your phone to fix a bug that lives in the update itself achieves nothing. For most people none of that is necessary, because the warmth fades on its own once the phone has finished rebuilding what the update changed. The pattern is what tells you which situation you are in, since normal post-update heat eases week by week while a real fault holds steady or gets worse.
