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 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.
Read the evidence →
Teeth Grinding & Jaw
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.