there is a polish sold that when applied imparts a bitter taste when you put your fingers in your mouth. The same concept as the bitter spray used for pets. I dont know if this is the best way to do it...

Nail biting can be more than just a bad habit. It can be the result of a faulty cingulate system in the brain. Did you know that onychophagia (nail biting) is categorized as an obsessive-compulsive (OCD) spectrum disorder and can be the result of a problematic cingulate system? (The cingulate system is the part of your brain that deals with your ability to shift attention, cognitive flexibility--ability to adapt to change, deal successfully with new problems--adaptability, movement from idea to idea, ablility to see options, ability to "go with the flow", ability to cooperate--shifting attention and with getting stuck in innefective behavior patterns). In a fantastic book I read called Change Your Brain, Change Your Life by a man named Dr. Amen (a clinical neuroscientist, child and adolescent psychiatrist, and medical directer of the Amen Clinic For Behavioral Medicine), he talks about problems with the Cingulate System, which include (does any of this sound familiar to you?): --Worrying --Holding onto hurts from the past --Getting stuck on thoughts (obsessions) --Getting stuck on behaviors (compulsions) --Oppositional behavior --Argumentativeness --Uncooperativeness; tendency to say no automatically --Addictive behaviors (alcohol or drug abuse, eating disorders) --Cognitive inflexibility --Road rage --“I would also add oppositional defiant disorder.”~Dr. Amen --Obsessive Compulsive Disorder (OCD) --OCD spectrum disorders: "There is a group of disorders that have been recently labeled obsessive-compulsive spectrum disorders. People with these disorders get stuck on unwanted, repetitive thoughts and cannot get them out of their minds unless they act in a specific manner. According to psychiatrist Ronald Pies, postulated OCD spectrum disorders include: Onychophagia (nail biting) Tourette's syndrom (involuntary motor and vocal tics) Kleptromania Body dysmorphic disorder (feeling that part of the body is excessively ugly) Hypochondria Autism Compulsive shopping (repetitive thoughts like 'I need to buy this one thing! I need to buy this one thing! I need to buy this one thing!') Pathological gambling Chronic pain Addictive disorders Eating disorders (such as anorexia and bulimia--in which there are "repetitive thoughts that significantly interfere with behavior" like '''Im too fat! I'm too fat! I'm too fat!' despite rational evidence to the contrary") Trichotillomania (pulling out one's own hair) So perhaps your child's nail biting is a symptom of a faulty cingulate system, in which case, an antiobsessive medication might provide relief. According to Dr. Amen (at the time of his writing, in 1998) "there are eight "antiobsessive medications" and more on the way. The current medications that have shown effectiveness with OCD [and OCD spectrum disorders I assume] are Anafranil (clomipramine), Prozac (fluoxetine), Zoloft (sertraline), Paxil (paroxetine), Effexor (venlafaxine), Serzone (nefazodone), Remeron (mirtazapine), and Luvox (fluvoxamine). These medications have provided many patients with profound relief from OCD symptoms. In addition, behavior therapy is often helpful...." Maybe this information will be helpful to you for breaking your child's habit, if its more than just a habit. Love, Amy