Someone in every friend group can bend their thumb back until it touches their forearm, or straighten their elbows a little past where everyone else’s stop, and it never fails to make people wince. “Double-jointed” is the term everyone reaches for, but it’s a bit of a misnomer. Nobody actually has extra joints. What’s really going on is a genuine difference in the flexibility of the connective tissue holding those joints together.
What Causes Joint Hypermobility
Your joints are held together and stabilized by connective tissue, including ligaments and tendons, which are largely made up of a protein called collagen. Collagen provides structure and strength throughout your body, and small genetic variations in the genes responsible for building it, including several in the COL gene family, can result in connective tissue that’s naturally looser or more stretchy than average.
People with more flexible collagen structures often have joints that move through a greater range of motion than is typical, which is what allows for the classic party tricks of bending fingers backward, touching your thumb to your wrist, or hyperextending your knees or elbows slightly beyond a straight line. This trait, formally called joint hypermobility, tends to run in families, which fits with its strong underlying genetic basis.
Hypermobility Exists on a Spectrum
Most people with noticeably flexible joints fall into a category researchers describe as generalized joint hypermobility, which for the vast majority of people is simply a normal variation in connective tissue, similar to being naturally tall or having a particular hair texture. On the more uncommon end of the spectrum, a small number of people have hypermobility severe enough, combined with other symptoms, to be classified as a hypermobility spectrum disorder, or in rarer cases, a connective tissue condition like Ehlers-Danlos syndrome, which involves more widespread effects on the body beyond joint flexibility alone.
How Common Is Being Double-Jointed
General joint hypermobility is fairly common, and research suggests it affects a meaningful portion of the population, with rates tending to be somewhat higher in children and adolescents, and often decreasing gradually with age as connective tissue naturally stiffens over time. It also tends to be somewhat more common in women than men, for reasons researchers believe are tied to hormonal influences on connective tissue alongside genetics.
Does Joint Hypermobility Affect Your Health
For most people, hypermobility is a harmless, even fun, physical quirk. That said, more flexible joints can be somewhat more prone to sprains, dislocations, or general joint discomfort over time, particularly with repetitive strain or high-impact activity, simply because the connective tissue provides less natural resistance to unusual movement. Some people with significant hypermobility also report more frequent joint pain or fatigue, which is worth discussing with a doctor if it’s a persistent issue rather than an occasional ache.
If hypermobility is accompanied by other symptoms, such as unusually stretchy skin, frequent injuries, or a family history of connective tissue conditions, it’s reasonable to mention this combination to a doctor, since it can occasionally point toward one of the broader connective tissue conditions rather than simple generalized flexibility.
What Hypermobility Genetics Means for You
If you’ve always been the one showing off your bendy fingers at parties, your collagen genetics are very likely the real explanation, and for most people, it’s simply an interesting physical trait rather than anything to worry about. Knowing more about your connective tissue genetics can still be useful, particularly if you’re active in sports or activities where joint stability matters.
A home DNA test with a detailed connective tissue report can offer a clearer picture of your specific collagen-related genetics, which can help inform decisions around training, injury prevention, and simply understanding your body’s natural range of motion.
Frequently Asked Questions
Is Being Double-Jointed the Same as Having Extra Joints?
No, this is a common misconception. Everyone has the same number of joints. Hypermobility comes from more flexible connective tissue allowing a greater range of motion, not from any structural difference in joint count.
Does Hypermobility Go Away With Age?
For many people, yes, to some degree. Connective tissue naturally becomes less flexible over time, so joint hypermobility that was very noticeable in childhood or the teenage years often decreases somewhat in adulthood.
Are Hypermobile People More Likely to Get Injured?
Somewhat, particularly with repetitive strain or high-impact activities, since looser connective tissue provides less natural joint stability. This doesn’t mean injury is inevitable, but extra attention to joint support and strength training can be genuinely helpful.
Should I See a Doctor About Being Double-Jointed?
For most people, no, since it’s a normal and harmless variation. It’s worth mentioning to a doctor if it comes with frequent pain, injuries, unusually stretchy skin, or other symptoms that suggest something beyond typical flexibility.
So the next time someone bends their thumb back and makes the whole room cringe, you’ll know it’s not a party trick they practiced. It’s just collagen doing exactly what their genes built it to do.
