I sometimes do the same thing. Sometimes not even when I'm upset, but because my hands always need to be doing something. If you're stressed, you should find something to occupy your hands such as a stress ball or play-doh. You could also try drawing on yourself or writing something. In addition to being a distraction, your hands will also be occupied and you won't be able to scratch yourself.

distract yourself and cover them if need so you are not tempted

I hate the mess I make of myself but at the time it's just like a habit. Have had several courses of antibiotics because of infections and hate showing my legs arms and hands

I know it makes me feel yuck after I have done it though, I'm going to try and draw flowers around mine to see how I go

Oh and scabs! I love scabs! My own tho. Gross i know but it's so therapeutic