Nail/fingertip biting in 4 yr old.

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In the last couple of months my 4 yr old DS4 started to bite his nails. This has now progressed into biting the skin of the tips of his fingers causing them to bleed.

He is the youngest of 4 boys, 2 of whom are ASD, so it can be quite a stressful house but I can't think of anything obvious that would cause more anxiety than usual. He is also a "demanding", active child. We are also having trouble getting him clean (but that's another story).

I tried to use "stop n grow" on him but he just kept spitting out onto his sleeves. I can't use it now because he has broken skin on his fingertips.

Does anyone have any experience of this and any suggestions? I am very concerned about the fingertip biting - he is literally taking chunks out of his fingers (and some of his knuckles).

Thanks.

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