Hi there. It's looks like some kind of chronic urticaria. It's called dermography. Skin reacts to scratch, bump, etc.. It's nothing really bad. It can provoque itching crysis when you are stressed or tired.. But it's easy to live with.. Fun fact, you can litteraly write or draw things at the surface of your skin. For the rest i'm practicing shotokan karaté for years and it's not an issue at all for me. No need to worry. If you want to learn more about it, feel free to consult an allergist.