3yo pulling his own hair out! Anyone know about or experienced this?

[JoanCrawford]

I have a friend whose ds is doing this. I see her a few times a week and have noticed her ds doing this on occasions. I think it's an odd thing to do. It must hurt him. It's not 'clumps' of hair but, say, 4/5 strands at a time.

I'm worried about it tbh. Mentioned it to his mum who thinks it nothing to worry about. I hope she's right and that I'm being ott and dramatic.

What do you think?