I used to as a kid, but like someone said above, I had an 'epiphany' at about age 7-8yrs, after watching Mum painting and making a fuss of hers, and never did it again.

Another thing that Mum, my sister, brother and myself (and now DP) do is biting the skin on your lip, or picking it. Its a stress thing, and most of the time you do it subconsciously. I remember having a chuckle one day as there was me, Mum and Boo (short for Belinda) sitting in a row on the couch picking our lips.

As for whether it is learned or genetic, have a think about this one. My brother was brought up in foster care since he was 2yrs, as he had a few learning difficulties, and Mum had me her crippled DD to worry about. Now, he wasnt brought up with us or Mum, and yet when we caught up a few years ago, he does the same lip thing, AND but his nails like I did, as did Mum as a kid. Food for thought...

I think you are on to a good idea with the painting of nails, I remember the yucky tasting stuff only deterring me for a few hours, but I remember the sticker charts and rewards working well. But in the end it was just my choice to stop, but who knows if I would have without the support and encouragement from Mum?

 At the end of the day, it is a comfort thing, and one possible thing you may try (worked with a child I nannied for) you could take her shopping for a 'really special teddy bear' and when you find him/her, tell poppet that every time she feels like biting her nails, she can squeeze bears paw, and if she is old enough, she can whisper in teddys ear about how she feels when she wants to bite. It may be she is bored, or worried, or angry, frustrated... etc. she will soon find herself confiding in teddy, and squeezing that paw, and the nails should grow. It doesnt take long for them to grow and look lovely and this will be incentive for her to keep it up. And maybe you will be able to se what her triggers are after a while and help her avoid them. (sorry if it sounds a bit clinical, but Im studying child psychology atm, so I have a deep fascination with it)

Sorry for the long rant, and best of luck with the nail biting.

Like eomachine, I bit mine until I was an adult! I stopped when I had an 'epiphany' in Amsterdam at age 27!!! (You prob get the picture!!!) I used to bit mine until they bled, and rip the skin all down the sides, it was awful, and I was so embarrassed of them during my teenage years - but for some reason I never stopped.

My dad bit his nails, but my mum always had beautiful nails (I would spend hours as a child watching her paint them....) My mum tried everything to get me to stop, that yucky tasting nail polish didnt work - I would just get used the taste, tabasco sauce - didnt work either!

I think its a learned behaviour - I saw my dad do it all the time, and I also associated it with stress from quite a young age, so when I was stressed or nervous I would nibble....

I was constantly nagged by my entire family about it for years and years, but eventually it was just something I decided to stop doing myself.