Hand sucking and chewing...

My son chews and sucks on his hands so much that his little hands get chapped. I have tried keeping mittens on him but he pulls them off so quick.Trying to keep them on him is frustrating to both of us. Others have suggested that I try different toys to interest him in rather than his hands which I have done.It does not seem to be working either. It's almost as if all of the toys are so big he can not actually get them in his mouth.I can tell when he is holding it that he is trying to put the toy in his mouth but he gets most of his hand in his mouth instead. Is this just a phase or should I be concerned ?