Another nervous habit that’s really not good for you is chewing on your nails. “Biting your nails can result in damage to the nails and infection of the skin surrounding it, called paronychia,” Dr Ansari says. The spread of germs can work the other way, too. “In addition, this can introduce viruses into the body, resulting in upper respiratory and other infections,” he says. Dr Fowler says you could also damage your teeth, or even crack a tooth! Plus, the psychological reasons why you do it need to be addressed. “Biting nails is usually a subconscious habit frequently made worse by anxiety,” Dr Fowler says. “What is making you so anxious? Anxiety itself may not be dangerous, but it can affect the quality of your life.” A study from Canada found that nail biting is also caused by boredom and frustration – two traits of perfectionists, according to the research.