There exists only limited research on this topic. Maybe the most famous article was published in 1995 in the Journal of Clinical Psychiatry. The authors made a questionnaire on habitual nose picking. Only about 250 out of 1000 addressed adolescents answered the questionnaire (so it is not very representative). However, 91% wrote that they frequently picked their nose. About 9.2% said it was "more than average".

A severe problem only occurs if nose picking causes severe impairment of daily living or medical problems (like nose bleeding) and if you cannot control the habit yourself.
There was no clear cut-off for the time patients spend nose-picking. I think anything more than an hour a day should warrant professional treatment. About 18% of the adolescents reported nose bleeding and 0.8% reported damage of the nasal septum due to habitual nose picking.

It is important to evaluate the "effect" of the habit for the individual. Most clients do it to relieve discomfort or itchiness (about 66%), 17.2 did it due to a habit

If you think of other psychological problems that might be related to rhinotillotexomania, other disorders of the obsessive-compulsive-spectrum like Trichtotillomania, nail-biting or other related problems, may come to mind.

To describe the problem in a simple way: People with Rhinotillexomania cannot inhibit their habit. This is usually a neurobiologically based problem!

People with OCD or related disorder usually feel anxious or very tense if they are not allowed to indulge in their obsessive habit. It helps to get short-term relief but they are not able to control and inhibit this behaviour. Usually a combination of medication (using SSRI = Selective Serotonine Reuptake Inhibitors) and cognitive-behavioural therapy is helpful.

Other patients with habitual nose picking might have a motor tic or Tourette's Syndrome. This is a neurobiological disorder (with alteration of the inhibition center of the brains). There are special treatment options including some neuroleptics and psychotherapy.

I am also aware of some clients that try to use a kind of self-stimulation due to lack of attention. People with ADHD (Attention-Deficit-Disorder) very often feel nervous and might use nose-picking to get relief keep their brain "awake".

Psychotherapy can offer different ways to help patients with this kind of problem:

1. Coping
   Psycho-education about the causes and prevalence of the problem and ways to cope in everyday life might be helpful for most patients.
2. Relaxation
   There are different ways to reduce stress and tension. Usually habitual problems are more severe if people are stressed. Learn muscle relaxation or any other kind of relaxation therapy.
3. Habit reversal
   This is a special technique used to block unwanted habits. You learn to be specially aware of the habit and block it with another habit (like crossing your fingers or pressing the finger on your leg) which is incongruent with the unwanted habit. (More information about habit reversal at http://www.dbpeds.org/articles/detail.cfm?TextID=37

In some cases, an ointment which stops itching in the nose might help. Some people have found that mild hydrocortisone ointments or anti-biotic ointments containing fusidic acid help. You could discuss this with your doctor.