Health consequences
Biting nails can lead to broken skin on the cuticle. When cuticles are improperly removed, they are susceptible to microbial and viral infections such as paronychia. Saliva may then redden and infect the skin.[2]
Nail biting is also related to dental problems, such as gingival injury and malocclusion of the anterior teeth.[3][4]
It can also transfer pinworms or bacteria buried under the surface of the nail from the anus region to the mouth.[5][6] When the bitten-off nails are swallowed stomach problems can develop.[4]
Medical literature reports cases of fingernails being severely deformed after years of nail biting.[7]
Treatment
The most common treatment, which is cheap and widely available, is to apply a clear, bitter-tasting nail polish to the nails. Normally denatonium benzoate is used, the most bitter chemical compound known. The bitter flavor discourages the nail-biting habit.[8] Mouthpieces that prevent nail-biting are also available.[9]
Behavioral therapy is beneficial when simpler measures are not effective. Habit Reversal Training (HRT), which seeks to unlearn the habit of nail biting and possibly replace it with a more constructive habit, has shown its effectiveness versus placebo in children and adults.[10][11] In addition to HRT, stimulus control therapy is used to both identify and then eliminate the stimulus that frequently triggers biting urges.[12]
Finally nail cosmetics can help to ameliorate nail biting social effects.[13]
Children can wear footed pajamas as a reminder not to bite their toenails.[14]