Today, News.com.au ran a story: "Pregnant mum burnt by iPhone 7". A woman has apparently suffered superficial burns from what she says was an overheating iPhone, despite the phone itself being designed to cease charging and power down before any dangerous temperature is reached. It's a terrible thing to happen to anyone, but let's take a lesson from this: don't fall asleep with your phone anywhere near you.
I'm a bit conflicted about this story, to be honest. It shouldn't have happened. Modern smartphones have dozens of different sensors to prevent overheating during regular usage or during charging. Any smartphone that you can buy in 2016 should turn off long before overheating to the point that it would leave a mark on the user's skin. An iPhone overheating while charging is not something that should happen, and not something I've heard any significant number of reports of in the past.
Apple's charging methods, too, are not anywhere near as fast or powerful — in terms of outright wattage delivered from the wall charger through — as some of its competitors, making the overheating even less likely. A properly manufactured charger will deliver a stable current and will, in concert with the phone, slow charging when a phone heats up or the battery reaches the limits of its capacity to prevent battery damage. Apple's chargers are expensive because they're good.
The small wall-wart USB chargers bundled with iPhones are only capable of 5 watt (5V 1A) power output, a far cry from the up to 25 watts (5V 5A) of the fastest charging phones in Australia — currently a title held by Oppo's VOOC Flash Charge. It's widely speculated that Samsung's Galaxy Note7 battery fires were due to fast (18 watt) charging overheating the batteries without the correct safeguards in place. But Apple's charging just doesn't have the juice to heat up a phone to skin-burning levels.
We don't know the full facts, but there's a chance that the charger in question was not an official Apple one, and was potentially delivering a higher wattage than the iPhone supported. I've written in the past on the dangers of buying cheap knock-off USB chargers and cables. They have killed people in Australia in the past. You should not be using a charger that does not have the Regulatory Compliance Mark.
Similarly, cheap cables — you know, the kind that you can buy five off eBay for a dollar — are equally dangerous. From my best guess looking at the images on Facebook, the 'burn' appears to snake along the woman's arm, suggesting that not only the phone but the Lightning-to-USB charging cable as well overheated to the point of branding her skin. Cheap cables can deliver deadly electric shocks.
Again, it's not something that should have happened with all the correct safeguards in place, but a short circuit or a poorly or cheaply wired charger or cable without the correct internal hardware — yes, Apple cables have their own internal circuitry to report and regulate voltage — could lead to this kind of thing happening.
But accidents and aberrances and one-off accidents happen, so let's give the story the benefit of the doubt, even if everything in the equation was end-to-end Apple and correctly . That aside, there is one thing that this incident should teach you: don't sleep with your phone. Even if all the safeguards from charger to cable to smartphone fuse and sensors and monitoring software are all in place, there's still no good reason to. Just finish looking at Facebook before you settle down for the night, put your phone on the bedside and get a proper night's rest.