Does scratching an itch on your head cause permanent hair damage to the follicle there for causing permanent hair loss?

No: Genetics cause permanent hair loss. If you are scratching and getting hair to break / fall off, then you may have a dermatological condition that needs exam and treatment (your Dr or a Dermatologist), but should grow back once resolved.

Everybody scratches: Long-term compulsive excoriation of an area of the scalp will cause permanent, scarring hair loss in that area. Ordinary scratching will not do this.