Is knuckle cracking harmful?

The straight answer is "No". Many people have misconception about it. The interphalangeal and the metacarpophalangeal joints in the fingers are the easiest joints to crack. The "popping" sound is thought to be gas bubbles imploding and collapsing in the synovial fluid that surrounds the joints. Knuckling is annoying, but it actually does not cause arthritis.

Someone might have fed you this myth because they could not stand the annoying sound. The popping noise you hear is not bone on bone — it is the bursting of small gas bubbles in the joint. And studies show there is no link between the habit and stiff, painful joints.