Brief Answer:
The condition is known as onychophagia

Detailed Answer:
Dear XXXX,
Thanks for using healthcaremagic.

I read your query and understand that it is very difficult to get rid of this habit. For a long time it was considered as a bad habit but recently experts opine that it is more than bad habit. Few of the experts classify it as a part of obsessive compulsive disorder and advocate treatment on similar lines.

Although this starts due to sense of insecurity but over time becomes a disorder which is difficult to get rid off.

I am also of the opinion that it should be treated by medication or behavior therapy used in the parent disorder of nail biting, otherwise known as obsessive compulsive disorder.

You can do the following things.
1. First decide that how much problem it is causing for you. Suppose it is costing more than one hour of your day than it is definitely needs treatment from the expert. As I said earlier medication especially SSRI group, like sertraline fluoxetine or Fluvoxamine group of medications are most effective in this disorder.

2. In case you find that it dose not cost your more than one hour in a typical day, than we can think of psychological interventions.

3. Try not to think about it. Keep yourself busy with one or another thing.

4. Keep your hands clean so the general health is not compromised due to this.

5. Whenever you get your fingers in your mouth, imagine a bad thing that you never like. With time you will be able to associate the imagined bad thing with nail biting and will able to overcome this habit.

6. Talk about it. Relax yourself and think of pleasant things in your life.

7. Meditation and yoga exercises.

8. Resolve the personal stress related issues as soon as possible

So to conclude both conventional and medical treatment is available for nail biting. You can chose which suits you most.

'Hope I have answered your query. If you have any further questions I will be happy to help".
Thanks

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