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SHOR T REPOR T Open Access
Prevalence of nail biting and its association with
mental health in a community sample of children
Ahmad Ghanizadeh
1,2*
and Hajar Shekoohi
1
Abstract
Background: This study evaluates onychophagia or nail biting (NB) prevalence and association with mental health
of a community sample of children from Shiraz, Iran.
Findings: The parents of 743 primary school children, selected by random sampling, reported NB behavior of their
children and themselves. Children’s mental health problem was assessed using the Strengths and Difficulties
Questionnaire (SDQ). 22.3% (95% CI: 19.3 to 25.3) of children had NB behavior in the last three months (girls: 20.1%
(95% CI: 15.9 to 24.2). The rate in boys was 24.4% (95% CI: 20.1 to 28.7). 36.8% of the children with NB had at least
one family member with nail biting. Older age was associated with a higher prevalence of NB while a higher score
on the prosocial score was associated with a lower prevalence of NB.
Conclusions: NB is a very common behavior in both genders in children and their family members. Children with
NB have less prosocial ability than those without it.
Findings
Nail biting (NB) or onychophagia is a common but
unresolved medical problem in children [1]. A study on
248 girls aged 15-16 years reported the rate of 25.5%
[2]. Another study on 385 school children aged 12-16
years using a questionnaire reported the rate of 29%[3].
Its incidence in the ages of 4-6 years is more than ear-
lier ages. Its rate increases in adolescence while it
declines in later ages [1]. NB is not gender dependent in
children less than 10 years but its incidence in boys is
more than girls in adolescents [1].
NB may induce complications such as malocclusion of
the anterior teeth [1], teeth root resorption [4], intestinal
parasitic infections [5], change of oral carriage of entero-
bacteriaceae [6], bacterial infection, and alveolar destruc-
tion [1]. Moreover, about one forth of patients with
temporo-mandibular joint pain and dysfunction have
nail biting habit [7].
Given that the treatment of nail biting is not easy.
Many of children with NB and their parents have
already tried to stop it but they were not successful.
Mayparentsmaypunishorridiculeorevenpressure
the children to stop it. But these attempts are not
usually effective in long term. Probably, the studying of
associated factors to NB helps us for planning more
effective managements [8].
At least, in clinical samples, NB reflects underlying emo-
tional disorders [9]. A study on clinical sample of children
showed that boys with NB suffer from at least one of the
psychiatric disorders more than girls that most likely were
attention deficit hyperactivity disorder (ADHD) 0.6%,
oppositional defiant disorder 36%, and separation anxiety
disorder 20.6%. The presence of psychiatric disorders is
not associated with the age of onset, the frequency of NB,
and the existence of physical damage [9]. NB is one of the
most common behavioral problems (228.6%) in children
and adolescents with Tourette syndrome [10]. Its rate in
children with ADHD is about 40.0% [11,12]. 14.3% of
children with alopecia areata suffer from NB [13]. It is sug-
gested that NB as a behavioral sensory processing problem
may help us for a better pharmacological management of
children with ADHD [14].
Moreover, more than half of parents of children with
NB have at least one psychiatric disorder most likely it
is major depression [9]. However, that study mentioned
that their sample was not typical of children with NB in
the general population. It recommended that future stu-
dies including community samples should be conducted.
* Correspondence: ghanizad@sina.tums.ac.ir
1
Research Center for Psychiatry and Behavioral Sciences, Hafez Hospital,
Shiraz, Iran
Full list of author information is available at the end of the article
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© 2011 Ghanizad eh et al; licensee BioMed Ce ntral Ltd. This is an open access article distributed under the terms of the Creati ve
Commons Attri bution License (http://creativecommons.org /licenses/by/2.0), which permits unrestricted use, distribution, and
reproductio n in any medium, provided the original work is properly cited.
The current cross-sectional study aimed to survey pre-
valence of nail biting in school aged children. The inves-
tigation of possible associating of NB with emotional
and behavioral problems is another aim of this study.
Materials and methods
The participants of this study are the parents of one
thousand school children selected by randomized cluster
sampling. 743 completed questionnaires were returned
by the parents. 358(48.2%) were boys and 385 were girls.
The parents reported their children’snailbitingbeha-
vior and his/her emotional and behavioral problems.
Parents reported the numbers of days per week whereby
the children bite their nail [9]. Parents were also ques-
tioned whether there is anybody else with nail biting
behavior in their family.
Strengths and Difficulties Questionnaire (SDQ)
The Strengths and Difficulties Questionnaire (SDQ) is a
research tool with adequate validity and reliability. It is
consisted of 25 items including five clinical scales:
hyperactivity/inattention, emotional symptoms, conduct
problems, peer relationship problems, and prosocial
behavior. Each of the clinical scales has 5 items.
Response to each item can range from 0 to 2. Zero was
for “not true”,1for“somewhat true’’,and2for
“certainly true”. Positive items are reverse coded except
for prosocial scale. So, the score of each clinical scale
can range from 0 to 10. Summing the scores from the
scales of hyperactivity/inattention, emotional symptoms,
conduct problems, and peer relationship problems gen-
erates a total difficulties score. The resultant score can
range from 0 to 40. Therefore, the prosocial scale is not
included for generating of total score. The parent ver-
sion of SDQ was used here. The psychometric proper-
ties of its Farsi version has been studied before [15].
SDQ takes about 5 to 10 minutes to be completed by
parents. Its scoring system is clear and straightforward.
Contrary to the other subscales of SDQ, higher score of
prosocial subscale indicates a better condition. SDQ is a
valuable brief screening instrument for the adjustment
and psychopathology of children [16,17]. The SDQ, its
Farsi language translation, scoring information, and pub-
licationslistcanberetrievedfromtheWebsiteof
http://www.sdqinfo.com.
Eight primary schools in the different geographic loca-
tions in the city of Shiraz, southern of Iran, were
selected by stratified random sampling method. All of
the principals of the schools agreed for participation in
the study after they were informed. They permitted us
to contact the parents. The questionnaire was delivered
to the parent by the students and then they completed
and returned back. Information about the aim of this
study was provided to the children and their parents.
Participation in this study was voluntary. The Good
Clinical Practice Guidelines, in accordance with the
Declaration of Helsinki, 1975, as revised in 2000 was
considered for conducting of this study. Parental con-
sent was provided by the parents of the children
involved in the study. This study was approved by Ethics
Committee of Shiraz University of Medical Sciences.
Statistical analysis
Statistical analysis was conducted using SPSS statistical
package. The frequency of nail biting by children and
their family members were analyzed for boys and girls.
t-test was used to compare the mean age of boys and
girls. Chi-Square test was used to study the association
of nail biting behavior and gender.
Logistic regression analysis was conducted to examine
association of the predictable factors and nail biting.
Nail biting was considered as a categorical variable. The
response categories of “never”and “I days per week”
was coded as zero and all other categories (i.e. >= 2
days per week) were coded as 1. The variables of age,
parental educational level, rank of birth, prosocial score,
emotional score, hyperactivity/inattention score, conduct
problem score, and peer problem score were considered
as independent factors. The educational levels of parents
were considered as continues variables.
Results
The mean age of the sample was 8.2(SD = 0.8) years
withtheagerangeof7to10years.Themeanageof
boys and girls was not different (t = 1.1, df = 741, P =
0.2). 358(48.25) of the sample were boys. 41.0% of the
children were the first child of their family. 28.4% were
the second child of family. 21.7% of the whole sample
was the only child. 38.4% had at least one brother or
sister.
The rate of nail biting in boys and girls was 20.1%
(95% confidence interval 15.9 to 24.2) and 24.4% (95%
confidence interval 20.1 to 28.7), respectively. The rate
of nail biting was not statistically different between boys
and girls (X2 = 1.98, df = 1, P = 0.1) (Table 1).
577(77.7%) of the parents reported that their children
have not habitually bitted nail in the last three months.
5.0% reported that their child frequently (more than
3 days per week) bitted his/her nail in the last three
months. The rate for children with 2-3 days and 1 day
were 7.1% and 10.2%, respectively. So, 22.3% of the sam-
ple had the habit of nail biting with frequency of at least
a day in week in the last three months. Out of the 166
children with nail biting, 45.8% of them bitted it 1 day
per week. The frequency of nail biting per day is indi-
cated in Table 2.
36.8% (95% CI: 22.3 to 44.2) of the children with nail
biting had at least one family member with nail biting.
Ghanizadeh and Shekoohi BMC Research Notes 2011, 4:116
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22.9% of children with nail biting have at least one
brother or sister with nail biting (Table 3). The parents
of 13.2% of children with nail biting habitually bite their
nail (Table 3). From 93 children with NB who has at
least one sibling, 31(33.3%) had a sibling with NB.
Totally, 53(55.8%) of children with NB who has at least
one sibling, at least one of their siblings or parents bite
his/her nail frequently (Table 4).
Table 5 indicates the mean scores of different domains
of parent reported SDQ for children with NB and those
without NB. It displays that the scores of prosocial
behavior score, emotional score and conduct score are
significantly different between children with and those
without nail biting. Prosocial behavior score in children
with nail biting is less than that those counterparts with-
out nail biting. Emotional problem score and conduct
problem score of children with nail biting are more than
that of those children without nail biting.
Logistic regression analysis indicated that the factors
of age of children and prosocial score have a statistically
significant association with nail biting frequency in chil-
dren. None of the parental educational level, gender,
rank of birth, hyperactivity/inattention score, conduct
problem score, and peer problem score significantly pre-
dicts nail biting frequency in children. There was a
marked trend for the association of emotional problems
and nail biting (Table 6).
Discussion
The most striking findings of our study are that emo-
tional and behavioral problems are more common in
children with nail biting than those without nail biting.
More than one fifth of children have this habit. In addi-
tion, our results added to literature that NB has a family
pattern. There was not a significant association between
nail biting and emotional problems, however, children
with NB have higher rates of emotional problems than
children without NB. In addition, the prosocial behavior
of children with NB is weaker than that of those without
NB. This behavior is age dependent but it is not gender
related.
Nail-biting allows children relieve their anxiety, loneli-
ness, and deprivation of safety feeling and love [18].
However, there is a controversy about the association of
anxiety, stress and NB [19,20]. In the current study, emo-
tional problems are higher in those with NB. It should be
noticed that emotional problems are not equal to anxiety.
In addition, possible cause and effect of anxiety and NB
has not already been reported. Meanwhile, 20% of clinical
sample of children with NB had separation anxiety disor-
der [9]. It is possible that both of them are secondary to
a common factor. Moreover, NB is a common co-existing
problem in many psychiatric disorders [10,21,22] and
these co-morbidities may be an explanation for the
higher rate of emotional problems in children with NB.
Another possible explanation for the higher rate of
emotional problems in children with NB may be due to
the consequences of NB. Social and family pressure for
stopping this behavior may induce or increase emotional
problems of these children. Maybe these children will
experience higher level of emotional problems in later
ages.
Children with NB especially boys had lower score of
prosocial behavior score. This scale indicates social rela-
tionship ability. So, the lower score of prosocial behavior
score is related to lower ability. This lower ability may
be another explanation for higher emotional problems
in children with NB.
The mean score for conduct problem in children
with NB was more than that of those without NB. But
Table 1 Frequency of parent reported nail biting
Frequency Boys Girls Total Significancy
Number Percent Number Percent Number Percent
Always (4 days or more per week) 18 5.0 19 4.9 37 5.0% X
2
= 2.6, df = 3, P = 0.4
sometimes (2-3 days per week) 21 5.9 32 8.3 53 7.1%
Rare (1 day per week) 33 9.2 43 11.2 76 10.2%
Never 286 79.9 291 75.6 577 77.7%
Table 2 The frequency of nail biting per day
Times per day Frequency Percent
1 to 2 97 58.4
3 to 4 34 20.5
5 to 6 8 4.8
More than 6 12 7.2
Total 151 91.0
The discrepancy between total number and the number of children with nail
biting is due to missing data.
Table 3 The frequency of nail biting in the siblings or
parents of children with nail biting
Family member Frequency Percent
Sister 17 10.2
Brother 21 12.7
Father 8 4.8
Mother 14 8.4
Nobody 103 62.0
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after considering the covariant factors, conduct pro-
blems score did not predicted nail biting behavior. The
association of NB and aggression has been reported
before [23]. However, they did not include covariant
factor.
Thepresentstudyassomepreviousstudyhasshown
that the prevalence of parent reported NB is not gender
associated [1]. It is clear that this study is a cross sec-
tional study and it investigates the association of NB
and children’s emotional and behavioral problems.
There are several research and clinical implications for
these findings. The research implication is that the com-
mon behavior of nail biting should be studies more,
although research and evidence on nail biting etiology
and its associations are becoming more available. One of
the clinical implications is that nail biting occurs fre-
quently in other members of family. So, the questioning
about nail biting in children and students can be consid-
ered as a screening question. Positive response may indi-
cate high probability for happening in other members of
family. So, child psychiatric nurses and school nurses
should be very careful about this behavior. They should
evaluate children with nail biting for screening of emo-
tional problems and less developed prosocial behaviors.
Another clinical implication is that the other family
members of children with nail biting should be evaluated
and screened for nail biting. Psychological evaluations
should not be limited on the children. So, it seems that
nail biting should not be considered as a simple habit.
There are many consequences for nail biting that should
be considered. For example, these children may require
to be referred for dentistry assessment. Our finding has
an important clinical implication for management of
these children. Habit reversal which is usually used for
their management is not effective in long term in many
cases. An explanation for this failure can be due to lack
of consideration of co-occurring emotional and beha-
vioral problems.
In conclusion, nail biting is a very common, age
dependent, but not gender related behavior in school
age children. NB is associated with lower prosocial skills
in the community sample of children.
Table 4 The prevalence of nail biting in family members
of children with NB who has at last one sibling (n = 93)
Family member Frequency Percent
Sister 14 14.7
Brother 17 17.9
Father 2 2.1
Mother 7 7.4
Total 53 55.8
Table 5 The comparison of the mean score of different domains of parent reported SDQ between children with nail
biting (> = 1 day per week) and that of those without nail biting
Scale Nail biting Mean Standard Deviation 95% Confidence Interval for Mean
Lower Bound Upper Bound
Prosocial behavior score Without 8.15 1.6 8.0 8.3
With 7.6 2.0 7.2 7.9
Hyperactivity/inattentiveness scale Without 5.5 1.6 5.4 5.7
With 5.8 1.7 5.5 6.0
emotional problem score Without 3.7 1.8 3.5 3.8
With 4.3 2.1 4.0 4.6
Conduct problem Score Without 2.9 1.4 2.8 3.0
With 3.2 1.4 3.0 3.4
Peer problem score Without 4.9 1.5 4.8 5.1
With 5.1 1.6 4.8 5.4
Total score Without 15.9 4.7 15.4 16.4
With 17.3 4.6 16.5 18.1
Table 6 Logistic regression analysis for the predictors of
parent-reported frequency of nail biting in children
Odds
ratio
95% C.I. Significance
Lower Upper
Age 1.5 1.12 2.07 .006
Gender 1.4 .81 2.44 .22
Rank of birth .8 .65 1.17 .36
Mother’s educational level 1.0 .90 1.13 .77
Father’s educational level 1.0 .99 1.19 .07
Prosocial behavior score .8 .75 .99 .044
Hyperactivity/inattention
scale
.9 .83 1.15 .81
emotional problem score 1.1 .98 1.32 .07
Conduct problem Score 1.1 .95 1.39 .14
Peer problem score 1.0 .85 1.20 .87
Ghanizadeh and Shekoohi BMC Research Notes 2011, 4:116
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Acknowledgements
This study was supported in part by Vice Chancellor for Research of Shiraz
University of Medical Science. There is no conflict of interest or financial or
other funding sources from each author to be declared.
Author details
1
Research Center for Psychiatry and Behavioral Sciences, Hafez Hospital,
Shiraz, Iran.
2
Department of Psychiatry, Shiraz University of Medical Sciences,
Hafez Hospital, Shiraz, Iran.
Authors’contributions
AG: Research project conception and organization. Statistical analysis design,
execution, review and critique. Writing the first draft and review and critique
of the manuscript. HS: Research project organization and execution.
Statistical analysis execution. Writing the first draft and review and critique of
the manuscript. All authors read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 28 February 2011 Accepted: 11 April 2011
Published: 11 April 2011
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doi:10.1186/1756-0500-4-116
Cite this article as: Ghanizadeh and Shekoohi: Prevalence of nail biting
and its association with mental health in a community sample of
children. BMC Research Notes 2011 4:116.
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