You pick up your iPhone and it's warm. Not just a little warm — genuinely hot. Hot enough that you set it face-down on the table and wonder if something is actually wrong.

Maybe it happens while it's charging. Maybe it happens when you're on a video call or streaming something. Maybe it's been happening more and more lately, even when the phone is just sitting there doing nothing.

If you've got an iPhone 15 or iPhone 16, you're not alone. This is one of the most common issues we see at MobileLizard right now. And the good news is — it's usually fixable. The tricky part is knowing what kind of problem you're dealing with, because not all overheating is the same.

Let's break it down.

First — Is the Heat Normal?

iPhones generate heat. That's just physics. Processors work, batteries discharge, screens light up — all of that produces warmth. There's a range of "normal" that Apple actually accounts for in the design.

So before we go any further, here's a quick honest answer: if your iPhone 15 or 16 gets warm while you're doing something intensive — long video call, streaming 4K, playing a game for an hour — that's expected. The phone should cool back down within a few minutes once you stop.

What's not normal:

• Getting hot while the screen is off and you're not using it
• Getting so hot it warns you and shuts down the display
• Running warm all day even with light use
• Overheating that started after a software update
• Heat concentrated in one specific spot on the phone

If any of that sounds familiar, keep reading. Here's what might be causing it.

Cause #1: Software — The Most Common Culprit

A lot of iPhone overheating that people bring to us turns out to be software-related. This is actually good news, because software problems are often the easiest to fix.

After a major iOS update, your iPhone doesn't just sit quietly. It's reindexing Spotlight, re-syncing your iCloud library, re-checking app permissions, running background tasks it deferred until after the update was stable. All of that runs the processor hard, and that means heat.

This kind of overheating usually settles down on its own within 24 to 72 hours. If your phone got hot right after updating to the latest iOS and seems better a day or two later, that's probably all it was.

The other software cause is runaway background apps. A single misbehaving app can pin your CPU at high usage without you knowing — which drains your battery, heats up the phone, and makes everything feel sluggish. Checking Settings → Battery → Battery Usage by App will often reveal the offender immediately.

Software Fixes to Try at Home

Cause #2: Battery Degradation

If you've tried the software fixes and your phone is still running hot consistently, the next thing to look at is your battery.

Lithium-ion batteries don't last forever. As they age, they become less efficient — they have to work harder to deliver the same amount of power, and that extra effort generates heat. A battery that's degraded to 80% health or below is working significantly harder than it should be. You'll notice it as a combination of heat, faster drain, and possibly unexpected shutdowns.

The iPhone 15 and 16 are now 1–3 years old for a lot of users. If you got yours at launch or close to it, there's a real chance your battery health has dropped into the range where it starts causing issues.

Battery replacement on the iPhone 15 and 16 is one of the most common repairs we do. It's same-day, usually takes 30–45 minutes, and it often makes a phone feel like new again — not just cooler, but faster and lasting longer on a charge too.

One thing worth knowing: Apple charges a premium for battery replacements and requires you to use their service process, which often means shipping your phone away or booking an appointment weeks out. At MobileLizard, walk-ins are welcome and we use quality replacement batteries that restore your phone's performance. Same-day. No appointment. Apple-like care without the Apple Store wait.

Cause #3: Charging Habits

How you charge your phone matters more than most people realize, and bad charging habits are a direct cause of overheating — and long-term battery damage.

The iPhone 15 and 16 support fast charging. That's great when you need power in a hurry, but fast charging generates significantly more heat than regular charging. If you're using MagSafe or a high-wattage USB-C charger and your phone is already warm, charging it will push the temperature higher.

A few things that make charging-related heat worse:

• Charging with a case on. Cases trap heat. If your phone runs hot while charging, take it out of the case first — especially thick silicone or folio cases.
• Leaving it on the charger 24/7. Keeping your phone plugged in at 100% constantly stresses the battery and generates sustained low-level heat. Optimized Battery Charging (Settings → Battery → Battery Health & Charging) helps with this, but it's worth knowing about.
• Using a cheap third-party charger. Off-brand chargers don't always regulate power delivery correctly. They can send inconsistent voltage to the phone, which causes heat and can damage the battery over time. Use Apple or MFi-certified accessories.
• Charging on a soft surface. Charging on your bed or under a pillow doesn't let the phone dissipate heat. Always charge on a hard, flat surface with airflow.

Cause #4: Hardware Damage — When It Needs a Professional

If your phone is running hot consistently, the heat is in a specific spot (usually the back, top right where the processor lives), and none of the software or charging fixes help — you may have a hardware issue that needs a repair.

Hardware-related overheating can come from a few places:

• A swollen or failing battery. If your battery isn't just old but actively degrading, it can generate heat on its own as it breaks down. If the back of your phone feels warmer than the screen side, this is a likely cause.
• Water or moisture damage. Water and electronics don't mix. Even the "water-resistant" rating on the iPhone 15 and 16 isn't water-proof, and moisture that gets inside can cause corrosion on the logic board that leads to all kinds of problems including overheating.
• Impact damage. If you've dropped your phone — especially if the back glass cracked — there's a chance internal components shifted or were damaged in ways you can't see from outside.
• A failing charging port or PMIC. The Power Management IC controls how your phone routes and uses power. If it's damaged, it can cause heat, battery drain, and charging issues all at once.

Quick Reference: Which Cause Is It?

One More Thing: The "iPhone 15 Overheating Bug"

It's worth addressing this directly. When the iPhone 15 launched in 2023, there was a genuine widespread overheating bug that Apple acknowledged. It was tied to the initial iOS 17 version and a specific Instagram app issue that was pushing the processor harder than intended. Both Apple and Instagram released updates to fix it.

If you're still on an older version of iOS, updating is the right move. But if you're fully updated and still experiencing heat issues on your iPhone 15, the most common explanation at this point is either battery degradation (they're now 2+ years old) or a charging habit issue. Both are fixable.

The iPhone 16 is newer, but we're already seeing units come in with battery health issues, particularly for heavy users who charge multiple times a day.