Biting off the skin on my fingers and on the joints. Any tips to stop?

As a little child I used to chew on my nails, mostly out of hobbit I believe. Eventually it got better and for some time I stopped biting on my nails completely. However I still continued to bite on the skin around the nail and along the edge of the fingernail. For sometime it became so worse that the skin I'm my finger became white and actually kind of wet since I constantly had the fingers in my mouth. Today I'm 13 years old and I still bite on the skin on my fingers(and sometimes the nails). I've noticed that I usually bite on my fingers when I'm in deep concentration without noticing it. The skin becomes hard and stiff and when I see it, it disturbs me and I want to peel it off which is the reason why I'm biting it. It's some kind of cycle. I've gotten almost like hard, round pads or bulges on my fingers and it looks horrible. Recently I don't bite as much since I've become more aware of it but those pads still won't disappear. I've had them for at least two years but they still won't heal. So does anyone have any tips on how to make them heal or disappear completely?