Pins and needles
Also called: Transient paresthesia · "My foot fell asleep"
The prickling, buzzing feeling in a limb after you sit on it or lean on it. It happens when blood returns to a squeezed nerve and its sensory fibres briefly fire on their own.
How common
Does this happen to you?
How it works
Sit on your foot, or lean on your elbow. The pressure squeezes the nerve and the small blood vessels that feed it. The nerve stops sending clear signals. The limb goes numb1. This numb stage has its own name, obdormition, which means “falling asleep”2.
Now lift the pressure. Blood returns. Myelinated sensory fibres that were starved of blood start to fire on their own3. They fire in fast bursts that start along the nerve, not in the skin3. The brain receives a burst of mixed signals with no clear source. You feel it as prickling, buzzing, or tiny needles1. The firing peaks within about two minutes, then slowly fades3.
Everyone with working nerves gets this. It is a normal nerve response, not damage.
How common it is
Pins and needles is the most familiar kind of paresthesia1. Most people have felt it at some point1. It is a predictable outcome of squeezing a nerve and its blood supply for long enough, not a trait some people have and others do not. Most cases come from an awkward posture held for a long time, such as sitting cross-legged1.
Try it
- Sit cross-legged on a hard floor for 10 to 15 minutes, or rest your elbow on a table edge.
- Notice the limb going numb and heavy.
- Stand up, or lift your arm off the edge.
- The prickling starts about half a minute later and peaks within about two minutes3.
- Move the limb gently until it settles.
Do not stand on a numb leg. It can give way under you. Do not hold the pressure for long.
Is it a problem?
Normal pins and needles pass within minutes once the pressure is off.
See a doctor if tingling:
- lasts for hours or days,
- comes with no pressure,
- spreads,
- comes with weakness.
Long-lasting paresthesia can point to a trapped nerve, low vitamin B12, or diabetes, and all of those can be treated1.
Sources and further material
- Wikipedia Paresthesia
- doi.org Paraesthesiae from ectopic impulse generation in human sensory nerves Nerve recordings in healthy people during post-ischaemic pins and needles.
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