Question: Unsurprisingly, the Lightning cable that came with my iPhone 5s ~18 months ago is really worn - to the point where all of the rubber cable has had to come off because it had been left around for a while and had gone all sticky (sooooo gross). The outer metal sheathing is still entirely intact.

The resulting cable looks like so.

[![It's a *little* bit worn](https://i.stack.imgur.com/L0eL1.jpg)](https://i.stack.imgur.com/L0eL1.jpg)

It still charges (and syncs) my iPhone perfectly. Is this at all dangerous to use (I'm charging my phone from my MacBook)?

Cheers,
Dan

Answer: 
Such Voltage is not 'dangerous' but you should get a new one as soon as possible. Why risk a further damage to your iPhone, your Mac or your charger?
Just underneath the plastic exterior of the cable is a conductive layer called shielding. Shielding is grounded, meaning it is connected to 0 V. It would only be dangerous if you had a serious electrical problem that caused ground in your outlet to be connected to a higher voltage potential. The actual power is transmitted on wires in the core of the cable. While the voltage at the core for iPhone charge cables is not typically dangerous, if the center of your cable becomes exposed, it's time to get a new cable.