Once you get old enough to stop sucking your thumb, your fingers really shouldn’t go anywhere near your mouth. If you’re eating finger foods with clean hands you should be fine — because your fingers aren’t actually going into your mouth — but we’d advise against licking your fingers after you’re finished. And as for biting your fingernails? That’s the dirtiest habit of all. Here’s why:
Your nails are filthy
Even after washing your hands, the undersides of your fingernails remain a hive of bacteria, fungus, yeast and other pathogens. Staph, a common cause of skin infections, is also prevalent.
It can ruin your teeth and gums
Constantly gnawing away at your fingernails is not a healthy use of your teeth. Constant nail biting can lead to dental chipping, tooth fractures, and even jaw displacement. Fingernail fragments can also become lodged under your gums, leading to serious infection.
It can destroy your nails and fingertips
Constant nail biting can damage the nail bed, leading to permanent nail damage (in some cases, nails may fall off and never grow back). Picking away at the skin around your nails can also lead to staph infections around your fingertips.
It can lead to grinding your teeth at night
The nervous habit of nail biting is very similar to teeth grinding, so one can easily lead to the other. Constant tooth grinding can wear your teeth down to the point where they fall out.
It can give you bad breath
Your mouth is already full of bacteria, but when you’re constantly sticking fingers into your mouth, it ups the bacterial load to really horrific levels — enough to make your breath noticeably worse than before. Not only is biting your nails a bad habit, it’s also one of many ways we bet you didn't know you were being rude.