Your hands and nails are loaded with bacteria, fungus, yeast and other harmful germs. When you put your unwashed hands and nails in your mouth, you are just increasing the risk of an infection.
Your nails are an ideal location for bacteria like salmonella and E. coli.
A 2007 study published in Oral Microbiology and Immunology tested 59 people to see whether nail biting had any real effect on transporting bacteria to the mouth.
The results show that Enterobacteriaceae were more prevalent in the oral cavities of children with nail-biting habits (76%) than in children with no oral habit (26.5%).
It can even increase the risk of warts and herpes infection.
When you bite your nails, harmful microbes are transferred from your nails to your mouth and make their way to your gut.
Once inside the stomach, these microbes can cause gastrointestinal infections that lead to diarrhea and abdominal pain.
Children with a nail biting habit are at a greater risk of digestive and enteric diseases like intestinal worm infections due to their weak immune system.
Nail biting also increases the risk of a nail infection. As you bite your nails, tiny tears or abrasions occur around the skin near your nails.
Harmful bacteria, yeast and other microorganisms can enter through these tears or abrasions, thus increasing the risk of infection.
The infection can lead to swelling, redness and pus around your nail, which can be difficult to treat if you do not stop nail biting.
According to the American Academy of Dermatology, biting your nails can lead to hangnails and make the skin around your nails bleed.
Apart from making you more susceptible to nail infections, biting your nails can cause severe damage to the nail bed, cuticles as well as the surrounding skin.
A 2011 study published in the Indian Journal of Plastic Surgery reports that nail deformities can be caused by subconscious habits like biting the nail as well as picking objects using the nail.
These habits cause elevation of the nail at the distal part and destroy the protection offered by the hyponychium at the distal end.
Chronic nail biting also can lead to irreversible shortening of the nails.