P.T.
If you want to help him stop try "Stop the Bite" made by Hoof. You can buy it at Wal Mart in the nail care isle. I only costs about $2.75 and taste really bad. I used it with my 4 year old and she stopped sucking her thumb almost over night. Also, try to talk with him and see if he can come up with another way to sooth himself when he is upset.