FormalPara Key Points

The prevalence of nail biting in 281 patients aged 3–21 years in an urban setting was 37%. A majority of biters reported a family history of the condition. Biters were also three times more likely to report a diagnosis of a psychiatric disorder than non-biters.

Increased efforts are needed to educate physicians on typical physical examination findings, underlying familial and psychiatric factors, and efficacious treatment options for pediatric onychophagia.

1 Introduction

Onychophagia, defined as habitual nail biting, is a common disorder affecting 6–45% of the population [1, 4, 5, 7,8,9]. The prevalence is likely underestimated, as patients may feel shame and, therefore, avoid seeking evaluation and treatment. Fingernails are bitten much more frequently than toenails, and typical physical examination findings are particularly short and uneven nail plates, absent cuticles, splinter hemorrhages, and eroded or scarred nail folds [10]. While onychophagia affects all age groups, it is more prevalent in children and adolescents, predisposing to psychosocial issues and complications including paronychia and dental problems. Onychophagia has been associated with anxiety and obsessive–compulsive disorder (OCD) in some studies [1, 2] but not others [3]. Further understanding of the prevalence, etiology, and co-morbidities associated with onychophagia is essential to diagnosing and treating affected patients. In this study, we sought to characterize the prevalence, presence of psychiatric co-morbidities, and effect of treatment of nail biting in the pediatric population.

2 Methods

An anonymous voluntary survey was administered at an outpatient academic pediatric clinic at Weill Cornell Medicine, New York, New York, USA. Patients aged 3–21 years were included if they or their parents were English-speaking and completed the survey in its entirety. A total of 282 subjects completed the survey and one patient was excluded due to incomplete data. When possible, patients were encouraged to complete the survey independently, though verbal administration and full or partial parent/guardian assistance was permitted as necessary, especially for those with inadequate reading comprehension. Guardians also independently verified the psychiatric history and specific diagnosis provided in response to the question ‘Have you ever been diagnosed with a psychiatric disorder?’ A copy of the survey instrument is shown in Electronic Supplementary Material 1. Study data were collected and managed using REDCap (Research Electronic Data Capture) electronic data capture tools hosted at Weill Cornell Medicine [11]. REDCap is a secure, web-based application designed to support data capture for research studies. Age, sex, psychiatric diagnosis, treatment sought, family history, and frequency of nail biting were analyzed in enrolled patients. STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) guidelines were utilized to ensure the quality of the reporting in this observational study [12].

3 Results

3.1 Prevalence of Onychophagia and Characteristics of Biters

In this study, 104 of 281 patients (37%) reported past or present nail biting for more than a month. Forty-nine biters were male and 55 were female. Patients began biting their nails at a median age of 5 years old (range 1–13 years). Most patients continued to bite their nails to present (Fig. 1). Slightly more patients bit their nails at least once a day (55/104) than less than once a day (49/104). Amongst biters, concurrent fingernail and toenail involvement was much less common (12%; 12/104) than that of fingernails alone (88%; 92/104). Among biters, 65 (63%) reported a family history of nail biting (Table 1).

Fig. 1
figure 1

Cumulative nail biting point prevalence by age. Incidence and resolution of past and present nail biting are depicted over the course of childhood

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Table 1 Nail-biting prevalence and biter characteristics
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3.2 Association of Onychophagia with Psychiatric Disorders

A significantly higher percentage of biters (18%; 19/104) than non-biters (6%; 11/177) reported diagnosis of a psychiatric disorder (p < 0.01). Moreover, those diagnosed with a psychiatric disorder showed a higher prevalence of nail-biting behavior (Fig. 2a). While toenail biting was quite uncommon overall, the ratio of fingernail and toenail biters to fingernail biters alone was greater in those with a psychiatric diagnosis (0.36) than without (0.09) (p = 0.07) (Fig. 2b).

Fig. 2
figure 2

Associations between onychophagia and psychiatric diagnosis. a Prevalence of nail biting in patients diagnosed versus not diagnosed with a psychiatric disorder; the former group comprised a higher percentage of patients reporting nail-biting behavior. b Distribution of nail involvement in biters diagnosed versus not diagnosed with a psychiatric disorder. A minority of biters reported co-morbid psychiatric diagnosis, but those who did reported both fingernail and toenail involvement at a higher rate than their counterparts

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3.3 Patient Awareness and Treatment of Onychophagia

Twenty-five percent of participants (26/104) sought treatment for their nail biting (Table 1). A multivariable regression analysis was conducted on the binary variable ‘How often do you bite your nails?’ against age, sex, psychiatric diagnosis, age of onset, treatment sought, distribution of affected nails, handedness, family history of nail biting, and feelings regarding the condition. Based on this evaluation, treatment for onychophagia had a significant effect (p = 0.03) and reduced the odds of frequent nail biting (at least once a day) by 64%. When subjects were asked ‘When are you most likely to bite your nails?’, 45 patients reported no particular reason, while 37 and 36 patients stated that they were bored or stressed, respectively. Less frequent answers were hungry (13) and other (six). Only 15% of biters (16/104) reported feelings of embarrassment associated with such behavior.

4 Discussion

Our study demonstrates that onychophagia is highly prevalent (37%) in the pediatric population, which falls on the higher end of previous estimates of 6–45% [1, 4, 5, 7,8,9]. Median age of onset was 5 years old, which is consistent with earlier studies reporting that nail biting was rare in patients less than 3 years old and decreased in prevalence after puberty [6, 13]. There was a slight predominance of female biters in our sample (53%), which is again consistent with that reported in previous pediatric and adult studies [5, 14, 15]. Furthermore, the majority of biters (63%) had at least one family member with the same habit; this exceeded that reported in a previous study (37%) [9].

Therefore, our data more firmly suggest that family members of biters should be screened for similar behavior. In addition, it may be beneficial to involve other affected members of the household in therapy. Importantly, biters were 3.34 times more likely to have a diagnosis of a psychiatric disorder than non-biters. Consistent with our results, a previous survey-based study showed that emotional and behavioral problems were more common in pediatric biters than in those not affected [9]. Furthermore, in two separate studies of children diagnosed with attention–deficit hyperactivity disorder (ADHD), 38–40% of children bit their nails [16, 17]. We also demonstrated that the ratio of fingernail and toenail biters to fingernail biters alone was greater in those with a psychiatric diagnosis (0.36) than without (0.09) (p = 0.09). Since the toenails are physically harder to bite than the fingernails, we postulate that there is increased urge and subsequent effort to bite at more distal structures. This finding has important clinical implications. First, it highlights the importance of performing a full skin examination including all 20 nails to uncover occult nail pathology. Secondly, toenail involvement should prompt clinicians to consider the possibility of psychiatric co-morbidity, which may or may not contribute to dermatologic pathology.

As described earlier, treatment of patients in our cohort—usually by topical application of bitter nail lacquers—produced significant improvement in terms of odds of frequent nail biting. In the literature, successful present-day management of onychophagia is built upon a combination of pharmacotherapy (including N-acetylcysteine or antidepressant administration), stimulus control, habit-reversal training, and cognitive–behavioral and aversion therapy. Particularly in children, N-acetylcysteine warrants consideration as an efficacious pharmacological intervention due to its relative safety [6].

Due to the wider implications of physical examination findings in biters, we propose that signs of onychophagia be emphasized as an integral part of the dermatology residency curriculum and certification examinations. CME (continuing medical education) manuscripts, lectures at local and national conferences, and inclusion in recertification examinations provide clinicians with avenues for career-long education in an important domain of dermatological care.

5 Limitations

This study is subject to several limitations. Our findings apply to children in an urban setting and may not accurately represent children in other environments. Additionally, while guardians provided independent verification of psychiatric diagnoses and history when applicable, diagnoses were self-reported without medical record confirmation due to the independent survey-based design. Therefore, these and other data may have been susceptible to inaccuracies for reasons related to embarrassment and general misreporting. Furthermore, a larger cohort and slightly different study design may have yielded enough subjects with particular psychiatric diagnoses (ADHD, anxiety, autism, etc.) to allow for analysis stratified by specific disorder with adequate power.

6 Conclusions

Onychophagia has a distinct clinical presentation and is highly prevalent in the pediatric population. Biters are more likely to report a variety of familial and psychiatric characteristics than non-biters. Therefore, psychiatric screening may be relevant in a subset of affected patients, especially ones with toenail involvement or other less common presentations. Increased efforts are needed to educate physicians on typical physical examination findings and available treatment options for pediatric patients with onychophagia.