Dear A Moment of Science: I am 12 years old and am double jointed. I have always wondered if this is a bad thing? --Flex
It's time to put to rest another common misconception. Though you can bend your thumb back and touch your forearm, there is no such thing as a "double joint."
Here's what's really going on. What we call "double jointed" is really just more-than-usual flexibility around a joint that results in a greater range of motion.
In other words, the joint is too flexible. It's common in children, and tends to be lost as we age.
No need to worry, just be careful. Too much flexibility can result in joint instability. The joint might move so much beyond what is normal that it can result in a dislocation, sprain, or ligament damage.
You can do exercises to strengthen the muscles around these "double joints" and this can help reduce the chance of injury.