I stopped (more or less) chewing up my fingers by using those blister bandaids to cover rhe ends of my nails.They are thick so protective, they last several days to a week, they don't come off like regular bandaids. After a month or so I got better at not starting to pick/chew and was able to stop the bandaids. I still carry a box with me because if I get anxious enough I'll still have to resist the urge to chew on my fingers. But I usually do resist and if I don't it's not nearly as bad as before.