Both unilateral and bilateral contracts are enforceable in court. For example, a unilateral contract is enforceable when someone chooses to begin fulfilling the act demanded by the promisor. A bilateral contract is enforceable from the get-go; both parties are bound the promise.
Yes, scratching is a form of self harm. Try to tackle this problem while you can because it has the potential to get worse. I started out scratching and now I burn myself with a lighter and cut myself. It's a self-destructive way to deal with overwhelming mental/emotional pain.
Habitual picking of scabs is classified in the group of psychological disorders associated with self-harm, such as deliberate skin cutting, head banging, and burning oneself. These actions are more often associated with girls than with boys and scab picking often starts when the subject is age 13 or 14. Psychological symptoms that are often associated with picking scabs are depression, low self-esteem, addiction, eating disorders, and anxiety.