Causes for Nail Biting and Thumb Sucking

Origin of Nail Biting and Thumb Sucking in Children

There are many causes for nail biting and thumb sucking in children. However most have a psychological origin. Both biting nails and sucking thumbs are often picked up during childhood. While these habits often dissolve on their own, there are cases where they continue into adolescence and even adulthood. It can help to understand the reason behind these habits in order to stop them early on, before they become a lifelong struggle.

What Causes Nail Biting?

The occasional act of biting nails in children is often no cause for concern. But when nail biting, or onychophagia, becomes a pathological disorder, there could be more reason for alarm.


Among the most common nail biting causes are stress and anxiety. It has been found that certain children, even as young as toddlers, naturally gravitate to biting nails when in a stressful environment or situation. It’s still unknown, however, what makes one individual more susceptible to this behavior over others.

boy with tie crying because of stress of nail biting


Nail biting is also more common when a child is engaged in an activity that requires great focus. While biting nails could help the child with their concentration, it’s also likely that they are simply under more pressure while they are in situations which require their undivided attention. This brings us back to stress at the predominant factor.

General Boredom

One of the other possible causes for nail biting is simply boredom. While some children lean towards swinging their legs or moving their bodies in other ways to relieve themselves of being underwhelmed, others may simply resort to biting nails.

kid sucking on finger next to baby

What are the Cons of Nail Biting?

Nail biting can be as benevolent as an occasional bite to the skin around the thumb or the nail itself. However, on the more extreme side, it can also be very damaging. Here are some possible consequences of prolonged nail biting:

  • Damaged skin, cuticles and general tissue damage
  • Deformed finger nails
  • Long-term issues with one’s jaw and bite, such as Temporomandibular Joint (TMJ)
  • Misalignment of teeth
  • Exposure to germs and bacteria
  • Greater susceptibility to chipping
  • Shame or embarrassment associated with this habit or the appearance of their fingers

What are the Pros of Nail Biting?

While biting nails can be detrimental in the long-run, the cause of nail biting psychology, especially in children, indicates the ability to self-sooth, which could be seen as a positive. With the nail biting causes being psychological in nature, it also seems that it does offer temporary relief. The important thing to remember is if this does become a long lasting issue, to start understanding how your child can stop biting nails permanently along with looking into next steps.

What Is the Cause of Thumb Sucking?

The act of thumb sucking is similar in nature to that of nail biting. As are the common causes for thumb sucking. The main difference between nail biting and thumb sucking being that the instinct for babies to suckle is key to their survival and a completely natural phenomenon. Infants have been found to suckle even while still in utero. So while nail biting is a habit that is picked up, thumb sucking is a more natural instinct that is often carried from infancy into childhood. And like nail biting, thumb sucking usually comes to an end on its own.


Aside from the natural instinct to suckle, the other main causes of thumb sucking, or the continuation of it, are anxiety and stress. Much like with nail biting, children most often adopt or prolong this habit when seeking ways to soothe themselves in stressful situations. Because suckling is so soothing during infancy, it makes sense that children naturally gravitate to thumb sucking as a comfort even later on in life.

What are the Cons of Thumb Sucking?

Although this instinct is natural, thumb sucking can be detrimental to a child’s overall health if prolonged for too long. Excessive thumb sucking has been known to lead to:

  • Malocclusion, or tooth misalignment, such as open bite and over bite
  • Lisped speech and other speech impediments
  • Skin problems, such as cracked, dry or bleeding skin on the preferred thumb
  • Unwanted germs and bacteria, potentially leading to illness
  • Structural issues with the thumb itself, such as elongating the thumb over time
  • Embarrassment, shame and social issues

What are the Pros of Thumb Sucking?

Much like with nail biting, thumb sucking can be seen as positive in that it is a coping mechanism. There is a good possibility that it does help to reduce stress for some children, and is also a potential indicator of healthy self-soothing tendencies.


All in all, the causes for nail biting and thumb sucking have an origin in the natural human desire to seek comfort in uncomfortable situations. While we do not necessarily want to encourage these habits in our children, and don’t want them to rely on them for a prolonged period, these issues do tend to resolve themselves, and can be appreciated for the temporary ease they provide. To learn more about what you can do to put nail biting and thumb sucking to an end, take a look at our parent toolkit for more information.