until their joints make noises? Humans are weird. Why do we do this?!

Yo nail-biters, Trace here for DNews, what's up? Pia Hansen sent us a good question recently,

about why people develop weird habits like nail-biting and knuckle-popping.

So, I looked into it!

Firstly, nail biting is a bad habit, but unless it becomes extreme, it's probably not harmful.

If it's a regular, pathological thing, it can become what's called "pathological grooming."

Which is uncontrolled, extreme grooming behaviors, like nail biting, skin picking, or hair pulling.

On the other hand, or… the OTHER hand… Scientists only recently learned

what cracking your knuckles is actually DOING inside your fingers. The sound is caused by "cavitation via tribonucleation…"

Basically, gas dissolved in the fluid between your joints forms a bubble,

and the sound is caused when the bubble FORMS, not pops.

And though it's weird lookin', scientists don't think it's actually harmful.

But the underlying question, as I see it, is why we have ANY HABIT at all.

Neuroscientists have tried to figure out where habits come from, and traced the path back to a part of the brain

called the basal ganglia -- it's connected with coordination and movement.

It's likely not the only system involved, because habits are complex behaviors,

but numerous studies, keep coming back to the ol' BG.

From a psychological perspective, a habit needs a few things to form: a trigger, an action, and a reward.

Together, they form a habit-loop. The habit loop is built on the

idea that at some point, you got a reward for doing the action in the first place.

For example: let's say you have a hangnail, it hurts… you pick at it, but it just hurts more…

so you pull it out with your teeth! Boom no more hangnail, no more pain! Trigger, action, reward!

Simple behavioral training. Finger cracking could be the same, though

the reward is somewhat more nebulous… Dr. Rachel Vreeman told NBC News, it could just

be a "physical release!" Maybe it just feels nicer? Or maybe you just like the noise!

How that one moment of pleasure turns into a habit is through repetition.

If you bite a hangnail enough times, you'll stop thinking about biting your hangnails, and then you have a habit.

Our brain is lazy, so if we can offload a task to our subconscious, we're going to that!

And once a habit is established, we stop thinking about it. Like, literally,

we stop sending the behavioral activity from the basal ganglia to the prefrontal cortex. The PFC is where we make decisions…

so if we're not engaging that part of our brain, we're literally not "thinking about it" before we do it.

Commonly, this can take from 15 to 254 DAYS of training.

Most of the time, if a habit isn't physically harmful, it’s just considered a bad social habit,

but if a habit creates open wounds or sores, begins wearing down your teeth,

someone is literally pulling their hair out… doctors can diagnose it as a psychological condition.

This means your brain has likely paired nail-biting, for example, with relief of anxiety or stress.

Damaging, compulsive nail-biting is called onychophagia,

and it's referred to as a "stress removal habit" by the Indian Journal of Dental Research

and appears on the spectrum of Obsessive Compulsive Disorders in the DSM-V.

Why some people pair stress relief with a habit isn't entirely clear.

But a 1970s twin study found there may be a genetic link.

Nail biting was practiced by nearly one-third of the 338 pairs of twins, and more in girls than boys;

and it was more common in twins who came from the same zygote!

Habits CAN be broken, but it takes work! You simply have to remind yourself to run your actions BACK through your prefrontal cortex!

That's why your mom put bandages or hot sauce on your fingers to keep you from biting your nails --

it reminded your brain, hey, pay attention, you could kick this habit! I don't bite my nails, but I DO I shake my leg a lot, like… a LOT a lot.

But why do we fidget? What's up with that? Luckily, some handsome devil looked into it over here.

A 130 years ago, people fidgeted. It's definitely not caused by over-caffeniated, ADHD-prone, coddled millennials.

Instead, fidgeting seems to be part of human nature. Are you a nail-biter? A finger-popper? Do you have tips to stop?

Share 'em here and ask us more science questions with the hashtag AskDNews! Thank you for your watching. See you next time.