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Chewed fingernails
Classification according to ICD-10
F98.8 Other specified behavioral and emotional disorders beginning in childhood and adolescence
F98.81 Onychophagia
S69 Other and unspecified injuries to the wrist and hand
ICD-10 online (WHO version 2019)

As onychophagia is called chewing or On ( fr ) eat the nails , claws or claw in humans or animals. Other terms for this are fingernail chewing , nail biting , nail biting , nail biting.

In humans, the more severe forms fall under the term “self -harm ”, although the lighter forms, which are based on nervousness, are not necessarily counted as self-harm . The causes are stress, nervousness, behavioral disorders or nail-biting role models. In damaged areas, vulgar warts are more likely to spread in humans . It is often associated with chewing the surrounding skin ( perionychophagia ).

Excessive nail biting was included under the umbrella term of so-called "body-related repetitive behavior disorders". It is similar to compulsive disorder and ranks mainly under the OC spectrum disorder .

Chronic anxiety disorders are blamed for this behavioral disorder in dogs. In sheep, on the other hand, onychophagia is not self-harm, but a form of cannibalism . Claws, ears ( otophagy ) and tails ( caudophagy ) of young animals up to one week old can be eaten by conspecifics . In addition to behavioral disorders, deficient feeding is also discussed in dogs and sheep.


Human medicine

Fingernail chewing can occur in neuroses or together with onychotillomania in paranoid psychoses . It is also found in restless, easily excitable and over-anxious children; then especially in stressful or conflict situations.

Those affected themselves report onychophagia in connection with behavioral disorders such as ADHD . According to this, biting fingernails for hyperactive people can be a satisfaction of needs in psychological rest phases or when bored. In the hyperactive, mental idleness triggers an inner restlessness, reluctance and tension that must be averted. One conceivable behavior to resolve these negative feelings is onychophagia.

Like all behaviors, onychophagia can also be learned in the context of model learning and, conversely, can be unlearned again. Children in particular can succumb to biting their fingernails if there are people in their personal environment who bite their fingernails and who represent a role model for the child (e.g. close relatives).

Veterinary medicine

In dogs, there is often a chronic anxiety disorder and in sheep, in addition to behavioral disorders (e.g. due to year-round housing), various deficiencies are discussed as an additional cause.


Existing consequences of onychophagia such as chronic inflammation of the nail bed or nail growth disorders require an adapted, mostly local therapy in humans and animals.

Human medicine

In general, the focus is on educating the patient. In some cases, psychotherapy or local measures such as applying nail polish or other bad-tasting substances and wearing gloves and artificial fingernails can also be helpful. However, it is crucial for success that the measure is voluntary and in consultation with the patient. Self-help measures such as the decoupling method also show success according to a controlled study.

Veterinary medicine

In sheep, it is common to separate aggressive animals from the young and even to euthanize animals that have been severely damaged by onychophagia.


As with any habitual, negative behavior or illness, there are certain appearances or consequences. The consequences of nail biting can be quite different. 

Health effects

Probably the most widespread consequences of onychophagy are enormously shortened fingernails. This self-inflicted mutilation is caused by nibbling on the nails. Affected people reduce the natural nail growth until the nail is permanently deformed. It is not uncommon for the nail bed and the surrounding skin to be affected. The resulting injuries can promote the formation of fungi and warts, inflammation and bacterial diseases. In addition to destroying the fingernail, swallowing the leftovers can also cause stomach pain and digestive problems. In addition, there were individual cases of misalignment of the teeth and inflammation of the gums.  

Psychological effects

Many of those affected are well aware of their problems and are ashamed of them. This feeling of shame can go so far that they want to hide their fingernails continuously and are therefore exposed to great psychological stress. Feeling unwell is always divided into different levels and, in the worst case, can lead to severe depression, as social decoupling often takes place. 

See also

Web links

Commons : Onychophagia  - collection of images, videos and audio files
Wiktionary: Onychophagy  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. a b c d P. Altmeyer: Therapielexikon Dermatology and Allergology: Therapy compact from AZ. Springer, 2005, ISBN 3-540-23781-X , p. 649. (online)
  2. a b H. Zaun u. a .: Pathological changes in the nail. Spitta Verlag, 2004, ISBN 3-934211-69-0 , p. 21. (online)
  3. MH Beers u. a: The MSD Manual for Diagnostics and Therapy. Elsevier, Urban & Fischer Verlag, 2007, ISBN 978-3-437-21761-6 , p. 1217. (online)
  4. a b S. Schroll u. a .: Behavioral medicine in dogs: key symptoms, diagnostics, therapy and prevention. Small animal concrete practice book , Thieme Verlag, 2007, ISBN 978-3-8304-1065-2 , pp. 59 + 297. (online)
  5. a b c H. Behrens u. a .: Textbook of Sheep Diseases. Georg Thieme Verlag, 2001, ISBN 3-8263-3186-9 , p. 441. (online)
  6. Helmut Remschmidt (2011): Child and Adolescent Psychiatry: A Practical Introduction. 6th edition. Thieme, Stuttgart, p. 177.
  7. On the subject: Behavioral problems in children and adolescents (V. Faust). psychosoziale-gesundheit.net, February 13, 2013, accessed on February 13, 2013 .
  8. Steffen Moritz: Self-help for trichotillomania and nail biting (decoupling method). UKE Hamburg, December 9, 2019, accessed December 9, 2019 .
  9. Steffen Moritz, Andras Treszl, Michael Rufer: A Randomized Controlled Trial of a Novel Self-Help Technique for Impulse Control Disorders: A Study on Nail-Biting . In: Behavior Modification . tape 35 , no. 5 , September 2011, ISSN  0145-4455 , p. 468-485 , doi : 10.1177 / 0145445511409395 ( sagepub.com [accessed December 9, 2019]).