I started at five, biting my arms and hands. I remember being at infant school, sitting cross legged at morning assembly. I heard a girl behind me whisper to her friend next to her "Look at her, she's biting herself"
They were talking about me! I felt acutely embarrassed & silly. I didn't even realise I was doing it till I heard them talking.
I have almost stopped as an adult, but the urge does come over me occasionally, I pinch or bite I think about cutting but don't do it.

I blame my narcissistic mother for my behaviour.