Could be he’s allergic to the bedding material in his box. Or some food he’s eating is inflammatory. It could even be lack of sufficient snuggles: lots of animals will pick and gnaw and scratch at themselves if socially neglected.
So many questions on a single image. Why the red marks? Why is the laptop so old it has a XP (maybe Vista?) certified sticker but shows a recent Sonic game collection? The world may never know. Godspeed little hedgehog, may you go fast and eat plenty of chili dogs.