Ever since I was a small child, I would bite my nails and make them all painful and useless. My mother tried that bitter polish on me but all it did was make my mouth bitter for hours.
Eventually my habit extended to skin biting and picking. I would bite and pick till most of my fingers were red, raw and bleeding or oozing plasma. The more I did it, the more I wanted to stop but I just couldn't. I remember the worst time was in high school when eight out of ten fingers were so horrific looking that I was ashamed to use them.
Although I've stopped now completely (which was quite difficult) my fingers remain scarred and the nails look a bit uneven. The best thing that helped me stop was my desire to see how my fingers were supposed to look. I had never seen my thumb cuticle unbitten before the age of 17 and my goal was to make all my fingers perfectly untouched. Willpower and the desire to succeed as well as an absolute hatred of skin/nail biting/picking helped me to overcome the habit. Skin biting/picking and nail biting/picking caused me years of misery.
When you get a hang-nail. Rush to some nail scissors to cut it off before you start picking it. Picking it only makes it worse. I always have nail scissors nearby at home.
Fight the urge to pick scabs on the fingers. The best way for a scab to heal is to leave it alone. Anything else makes it worse. One of the reasons I picked and bit was because of my "desire" to make the sore or scab better a lot more quickly and to make it perfect. Doing anything other than leaving it alone will make it worse. Leave fingers alone.
If you can't stop yourself from picking, wear gloves even indoors. This may look strange but it's for the greater good.
The pleasure of having no pain in my fingers far, far out-weighs any "pleasure" I got from picking and biting them. I remember when something as simple as writing was complete agony for me because of my habit. No more.
Thanks for reading and good luck with trying to stop. It is possible.