Because sensing pain is at the skin, The doomed disbelievers will get fresh skin for their burnt out skin .The scientist who relatively recently discovered the ending of nerves at the skin, became a Muslim after reading about these facts in the holy Quran.
In the name of Allah most Gracious most Mercieful
lo!Those who disbelieve Our revelations, We shall expose them to the fire. As often as their skins are consumed We shall exchange them for fresh skins that they may taste the torment. Lo! Allah is ever Mighty, Wise.
Allah The Great indeed spoke the truth.
Reference : Chapter(4) Verse "56"
i.e. Chapter (IV) Verse "56"