Evidence library
Research library
Statistics and evidence pages on stress habits and the nervous system. Every figure is traced to a primary source, with methods and limits stated plainly.
Nail Biting & BFRBs
Habit Reversal Training for BFRBs: What the Evidence Actually Shows
In meta-analyses, behavior therapy built on habit reversal is the best-supported treatment for hair pulling, with a large effect near 1.4, well above medication.
Read the evidence →How Common Are BFRBs? Body-Focused Repetitive Behavior Prevalence Explained
Roughly 3 to 5 percent of people are estimated to have a body-focused repetitive behavior. See where that range comes from and how it compares with common habits.
Read the evidence →Nail Biting and Anxiety: What the Research Actually Shows
In one study 22.5 percent of nail biters met anxiety-disorder criteria versus 26.2 percent of non-biters, and no link was found. See the mixed evidence here.
Read the evidence →Nail Biting in Children: Prevalence, Age of Onset, and Developmental Course
About 22 percent of schoolchildren bite their nails, and reviews put the peak near 45 percent around adolescence. See the age it starts, how it changes with age, and study caveats.
Read the evidence →Nail Biting Statistics: Prevalence, Age of Onset, and What the Numbers Actually Say
Nail biting affects 20 to 30 percent of the general population across all ages. See measured rates in children and students, the age it starts, and study caveats.
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Teeth Grinding & Jaw
Bruxism Statistics: How Common Are Teeth Grinding and Jaw Clenching?
Awake bruxism is reported by about 22 to 31 percent of adults and frequent sleep bruxism by around 13 percent. See prevalence by type and age, plus what drives it.
Read the evidence →What Causes Sleep Bruxism? The Evidence on Grinding Teeth at Night
Sleep bruxism is driven mainly by brief sleep arousals, with genetics explaining about half the variation. See the evidence on arousals, genes, substances, medications, and stress.
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About this library
Each page separates primary studies from reviews, explains why estimates differ rather than averaging them, and states the limitations of the underlying data. Figures are survey or clinical estimates unless noted otherwise. Nothing here is a diagnosis, a treatment recommendation, or medical advice. See how we research for the full method.