Why Do We Get Pins and Needles?

Everyone’s felt it before. Cross your legs weird for too long or something and you either get that kind of numb feeling or like a bunch of little pointy feet are walking all over you. It’s pretty weird, and maybe it freaked you out as a kid or something. But why do we get pins and needles?

Paresthesia

Let’s start with deconstructing what the “pins and needles” feeling actually is. You’d probably be unsurprised to learn that “pins and needles” or “that weird tingly feeling” isn’t a diagnosis you can receive. The feeling is more technically called “paresthesia” (paraesthesia). This is most commonly experienced as that kind of numbness you get when you sit on your hand as temporary paresthesia. Beyond the sensation itself, paresthesia is broadly defined as having no apparent physical cause like a rash or bruise. If you want to experience a more acute form of paresthesia, you can go and knock your funny bone. 

Further Reading: What’s Up with the Funny Bone? | Why Is it Called That?

Healthwise, temporary paresthesia probably isn’t worth fretting too much about. Chronic paresthesia is also known as Berger’s paresthesia, Sinagesia, or Bernhardt paresthesia. These conditions are typically either caused by a problem with the nervous system or poor circulation. These problems have a wide range of causes as well. Typically as we age our circulation gets worse (since plaque just builds up in our arteries over time), which makes our favorite pins-and-needles sensation more common as we get older. 

You can also experience chronic paresthesia as a result of nerve damage or injury, which is probably unsurprising to hear. Bernhardt paresthesia, for example, is localized entirely into the outer thigh. It’s caused when the lateral femoral cutaneous nerve is damaged, typically because it gets compressed/trapped between your hip bone and where it connects to your spine. This can happen if you wear a tight belt and stand too much, but it can also occur as a result of seat belt injuries or complications related to diabetes.

Okay, but I probably didn’t damage my nerves by crossing my legs

Yeah, that’s a valid point. Humans probably wouldn’t still be around if we could give ourselves permanent nerve damage by sitting on top of our hands for like three minutes. 

We’ve addressed two things that might cause your limbs to fall asleep so far. It’s either a nerve thing or a blood thing. Turns out, temporary paresthesia can be caused by both. It’s also most commonly caused by pressure (which you typically get through compression). A study in 1946 found that all you had to do to induce pins and needles is raise your blood pressure so that it was above your systolic blood pressure. That broadly means your blood pressure is higher than the pressure your heart exerts against your arteries by beating. Practically, this means the feeling can be induced by compressing your arm or leg for a couple minutes. 

The strength of the numb feeling depends on how long you compressed your limb, which you probably didn’t need a scientific paper to explain. When your limbs are compressed long enough to fall asleep, you’re depriving them of blood flow. In turn, you’re depriving the nerves in that limb of blood as well, which makes it a lot harder for your nerves to keep sending signals back to your brain. It also means that your nerves are firing less as a result.

Once you relieve the pressure and your leg starts “waking up” again, you might notice the pins and needles come in stronger for a bit. That’s because your brain is starting to receive signals from your limbs again, and the nerves are firing indiscriminately as they come back online. 


Speaking of pins and needles, what about pinned animals and stuff here?

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