This is a bit of a sad headcannon I have, but surely Tails must have a lot of scars under his fur, right?
Back when he got bullied on Westside Island it was physical. Like how we see his bullies pulling on his two tails in one of the Sonic Origin cutscenes. I can't recall another instance of the franchise canonically stating or showing how bad Tails got bullied. But I don't think it was just the tails pulling. He probably got beaten up or got pelted by rocks and sticks. And whatever else cruel child bullies do. And after he met Sonic they got into a ton of fights with Eggman and his Badniks. Even when he would defeat a bot unscathed, punching and kicking metal would still hurt.
I think the part of his body that has the most amount of cuts and wounds are his hands. He is a very handy person after all. He is always making inventions and gadgets. And when you're constantly soldering, hammering, wiring, you're bound to hurt yourself no matter how skilled and experienced you are. Instead of taking breaks and letting his wounds heal, he just bandages them quickly and moves on like the wound and pain was never there in the first place. In fact, his hands are probably almost completely numb. Who knows if he still has his fingerprints.
On the outside he's a clean and soft child. But underneath is a mangled and hardened kid who never got to live like one.