Greetings. I pick my scalp when I become overly stress. It is not good for me to become too stressed or else I tend to present more symptoms related to OCD and dermatillomania. And it gets worse if I don't wash my hair with special shampoo to get rid of dandruff at least 2-3 times a week, though the bottle says that after a month, I should only need to use it once every week or two, but it doesn't work for me. I don't know where you pick at, but some strategies I use that seem to help are...
-Cut your nails as short as possible. It's harder to scratch when you have short nails
-Wear gloves. This will make it hard to scratch too
-If you scratch your scalp like I do, wear a hat. This one really helps

Not sure if the next part needs a trigger warning, but references to blood are made below. Don't read if that makes you anxious.

Those are just some of the strategies I use to help me prevent my scratching. But even by using these strategies, I will scratch an area until blood comes, and then move on. My worse time was when I scratched it so bad I needed to hold a paper towel for 15 mins because of all the blood coming from it. I pick at clumps of dead skin mainly, but if I have scratched a lot, I will pick at scabs that have developed on my head from my previous scratch episodes. I'll scratch anywhere, anytime. School, home, work. Scratch whenever I'm awake and I need to do something.

Hope some of the strategies help