I think a lot of us do it, and I know I've done it ever since I was a kid. But is it really actually bad for you? 

My Grandmother always told me it was.  She had arthritis, and her fingers were very thin, with larger knuckles.  She told me her knuckles were so big because she cracked them as a kid. She said it gave her the arthritis pain in her hands.  Of course, that scared the bejeebus out of me as a kid, but... it didn't stop me.

I just didn't do it in front of her, like that would, you know, exempt me.

Well, I still do it every day, and I don't have arthritis yet.  So I thought, I have the Information Superhighway now.  Why don't I just Find Out? I did some searching and according to the Harvard Health:

The "pop" of a cracked knuckle is caused by bubbles bursting in the synovial fluid — the fluid that helps lubricate joints. The bubbles pop when you pull the bones apart, either by stretching the fingers or bending them backward, creating negative pressure.

So okay, that makes it a little creepy to think about bubbles in my hands, but that's science for you.  You can't cherrypick your information.  So what about arthritis?  I looked a little further and found some information from Medical News Today that definitely made it personal:

Despite popular beliefs, several studies have concluded that cracking knuckles is unlikely to be linked to arthritis. Dr. Donald Unger researched his own knuckle-cracking, in response to complaints from his family. He cracked the knuckles of his left hand at least twice a day for 50 years, but not those of his right hand. Unger did not develop arthritis in either hand, and there were no differences between the two hands. He concluded that knuckle cracking was not linked to arthritis.

DAMN, DOCTOR DONALD!  You did this for FIFTY YEARS?! Just to prove a point?! Wow.  You are... extra.  But I like it.

Well, there you have it, then.  Crack away at those knuckles, you'll be fine.

.........Just don't think about the bubbles too much.

Crackingly yours,
Behka