Nail-biting is an obsession for many adults. According to research from the American Journal of Orthodontics and Dentofacial Orthopedics (AJODO), this habit may form due to psychological issues or simply persist as a difficult-to-break childhood behavior.

While saliva can negatively affect the skin around the fingers, the bacteria on your hands are far from harmless once introduced into the mouth.

According to Dr. Adam Friedman, hands are the source of countless pathogens you may not even be aware of. These germs can easily hide under the nails and spread to any area they come into contact with.

Regardless of its cause, this habit can lead to numerous health problems. Adam Friedman, pharmacist and professor of dermatology at George Washington University, explains that you may want to quit nail-biting once you learn about its harmful effects:Nail-biting is a persistent issue for many adults.

Nail Infections

When nails are bitten excessively, they are exposed to bacteria in the mouth. This often leads to fungal nail infections and other skin conditions. According to research from American Family Physician, the most common condition caused by nail-biting is paronychia — an infection that makes fingertips swollen, painful, and red.

Excessive nail-biting increases the risk of nail exposure to oral bacteria.

Nail Inflammation

The chemical composition of saliva strongly breaks down fats and other food substances. This makes it crucial for digestion, but also the reason why experts advise against licking dry lips — saliva only makes things worse. The same happens when saliva continuously contacts nails. Frequent nail-biting erodes the skin and causes inflammation around the fingertips.

Saliva contains chemicals strong enough to break down fats and food particles.

Impaired Nail Growth

Payal Bhandari, pharmacist and medical consultant at Uqora, notes that the skin surrounding the nail base is responsible for producing keratin cells, which regulate nail growth. Nail-biting damages this skin, disrupting keratin production. As a result, nails may grow abnormally, unevenly, become brittle, or even fail to grow altogether.

Nail-biting damages the skin at the nail base, interrupting keratin cell production.

Acne

Normally, bacteria under the nails do not cause serious skin issues. However, with the help of saliva, they can easily adhere to and contaminate other areas.

According to Dr. Jacqueline Bromberg, physician and researcher at Memorial Sloan-Kettering Cancer Center, Weill Cornell Medical College, New York, the face is most affected due to its skin sensitivity and frequent hand contact in nail-biters.

Acne can easily flare up if you frequently bite your nails.

Herpes

Oral herpes can quickly spread to the hands when you bite your nails. According to data from Bumrungrad International Hospital (Bangkok, Thailand), up to 40% of adults experience problems with this condition. Common symptoms include swollen, painful, and itchy fingers, sometimes accompanied by mild fever. Within 1–2 weeks, blisters and discharge may appear on the fingers, along with increased pain.

Oral herpes can easily spread to your hands if you bite your nails.

Dental Problems

Teeth are also at risk from nail-biting. Erin Sundermann, scientist and assistant professor at UC San Diego School of Medicine, who leads research on “The impact of daily habits on teeth,” explains that chipped teeth, fractures, and gum inflammation are all common problems faced by nail-biters.