Thumb sucking or nail biting in childhood and adolescence is associated with an increased risk of Crohn's disease: results from a large case-control study.

BACKGROUND

The hygiene hypothesis suggests that a reduction in microbial exposure contributes to an impaired immune response later in life and increases the incidence of immune-mediated diseases such as inflammatory bowel diseases (IBD). Thumb sucking and nail biting are two early habits that modulate the oral microbiota composition and antigen load.

OBJECTIVE

We hypothesized a lower risk of Crohn's disease (CD) and ulcerative colitis (UC) in adults with prior thumb sucking and nail biting.

METHODS

918 IBD cases and their 918 siblings without IBD were asked to fill out a survey containing 32 questions on environmental factors in childhood and early adulthood. Prevalence of thumb sucking and/or nail biting at the usually well-remembered time of (1) school enrollment and (2) coming-of-age ceremonies was the predefined combined risk factor of this study.

RESULTS

65% of the patients were female and 57% suffered from CD. About 49% of IBD patients but only 44% of their siblings reported thumb sucking/nail biting at the time of school enrollment or coming-of-age (

CONCLUSION

Contrary to our expectation and challenging the hygiene hypothesis, we found that common oral habits are not protective against IBD. Instead, nail biting at the time of school enrollment and coming-of-age was a statistically significant risk factor for CD in our cohort. Key summary