What you learned in school
Health classes taught that the habit of cracking knuckles would lead to arthritis and joint problems later in life. Students were warned against this behavior to protect their long-term joint health and prevent future disability. Teachers often told students that the cracking sound indicated damage to bones or cartilage. The message was that this seemingly harmless habit would cause serious consequences including swollen, painful joints and reduced mobility in adulthood.
What we know now
Health classes taught that the habit of cracking knuckles would lead to arthritis and joint problems later in life. Students were warned against this behavior to protect their long-term joint health. Multiple studies have found no causal relationship between knuckle cracking and arthritis. The sound comes from gas bubbles collapsing in joint fluid, not from damage to bones or cartilage. Long-term studies of habitual knuckle crackers show no increased rates of arthritis compared to non-crackers. While excessive force could potentially cause injury, normal knuckle cracking appears harmless.