Hi Ziggiz,
May I ask how old your child is?
I'm a 34 year old biter, my nails look horrible. I also bite the inside of my cheeks, check your child's. I cannot remember a time in my life when I did not bite my nails, think it started when my parents divorced when I was about 2, but my mum doesn't really talk about it and never sought help when I was young.
I have to say that I have tried everything bar hypnosis. The bitter stuff doesn't work, I have had acrylic nails 'till my own had grown, continued biting when acrylic nails removed, etc. Here would be my top tips:
-older child, buy them a nail grooming kit and interest them in caring for their hands, even a boy, girl, perhps some nail varnish/bracelets etc?
- don't make a negative issue about it, don't be nasty/shame your child, my mum did this, I think it made it worse
- I bite when I'm stressed/anxious/bored, even though it hurts, as if I have to, almost compulsive, it's kind of soothng, iykwim. Reading that back sounds terrible, but it's true. Did something happen to trigger it? Is your child particularly anxious? I'm not anxious on the outside, I kind of channel it by biting my nails, if that makes any sense.
The best result I ever had when trying to stop was when I repaced the imuplse to bite with something alse. I always kept a bottle of hand cream with me, and when I wanted to bite, I applied a tiny drop of cream to my hands and massaged my nails instead. Best cream is Vaseline Intensive Care Hand and Nail, I found that it's the only cream that also strenthened the nail, and I went through LOADS of cream. My nails are very thin as I 'peel' the layers off too... don't ask. That worked best, managed to have 'long' nails for a year using that method. But I suppose it really depends on how old your DC is. How about installing a game on a phone or something, and if he/she wants to bite, to play the game instead? You need to replace the urge to bit with something else.
And praise praise praise for even the slightest sliver of white nail.
Wishing you all the best, very difficult habit to kick.