skin picking and chewing?

Ever since I stopped sucking my thumb aged about 10 all I can do is pick and chew at my skin. I don't think it's self harm because I'm not interested in mutilating myself at all, it's just a subconscious habit that I can't stop. When I'm on the computer I'll absent-mindedly chew big patches of skin off my thumb until the skin is red raw, and I peel great strips from certain areas of my heel, as well as picking skin from my thumbs and all around my fingernails. I absolutely cannot stop myself because I don't realise I do it but it's getting to the point where family members and friends shout at me all the time, and it's been brought to my attention just how much I do it. I've tried putting socks on my hands, and lotion on my feet but nothing seems to work. I think of it as just 'tidying up' the skin on my hands and feet but it's just making them red and sore. What can I do to stop?