I found a very effective way to stop this.
After close to 40 years and trying ABSOLUTELY EVERYTHING I tried INOSITOL due to a psychmed article I read about trich. (obsessive hair pulling) and thought "hmmm inositol's a harmless B vitamin, what could it hurt..."
Well, after only about 3 weeks of taking it in powdered form and immediately starting at the 18 gram max. amt. for this kind of problem (I was not under a doctors recommendation - and I took it randomly, sometimes 3 grams a day sometimes 18 due to forgetfulness and time constraints) while making a conscientious effort not to bite, I had completely stopped.
After only 3 weeks.
2 more weeks of 3 grams here and 18 there, with a day or two here and there completely missed altogether, and I stopped taking the Inositol too.
It's 2 years later and except for the abuse of 1 nail, always the same name oddly, only done twice during these 2 years... I now have very long, surprisingly strong, nails.
My only "maintenance" is that I now take a multi-vitamin religiously every single day.
I have no idea why it worked (supposed to effect your seratonin levels?) or what my "underlying" problem was as to why I had to bite them so miserably. Family, friends and doctors alike only offered the "If you really wanted to stop you could..." sage advice.
Mind you, my nails were nearly non existent. Seriously.
My "loving" older sister used to tell me daily that if I didn't stop I would "get cancer".
She didn't say it in a nice or "scared straight" kind of way either.
hmmmm....anyway....
I know I tried absolutely everything to stop.
40 years later....This WORKED.
LouisaJane said that she managed to stop while pregnant and I'm inclined to believe that her taking her PRENATAL VITAMINS, loaded with all sorts of mega doses of B vitamins, I suspect was the result of her declining need to bite her nails.
Try Inositol in it's powdered form.
It's harmless as it's not absorbed into your fat cells like vitamin A is so it's not toxic, side effects (like diarrhea) are easily manageable and go away after a day or two. Just stay hydrated if it happens to you.
Here's the psychmed article I read:
http://westsuffolkpsych.homestead.com/skinpicking.html
Good Luck.
This horrid "habit" can be surprisingly easy to cure.
I only wish that people had taken it more seriously 30 years ago.
Every year that goes by with you thinking your kid has a "bad habit" is a year of reinforcement for this "bad habit" to take hold, and could've been easily stopped all together for me 30 years ago.
http://www.medhelp.org/posts/new/503636#