Numbness in the shoulder, medically known as paresthesia, describes the feeling of tingling, prickling, or a complete loss of feeling. This sensation arises when the electrical signaling of nerves is disrupted, typically due to irritation, compression, or a temporary lack of blood flow. The shoulder area is supplied by the brachial plexus, a complex network of nerves originating in the neck. Because the nerve supply is extensive, the cause of numbness can range from a harmless, transient event to a sign of a more significant underlying condition involving the spine or surrounding anatomy.
Positional and Temporary Numbness
The most frequent reason for shoulder numbness is temporary interruption of nerve function or blood supply. This transient condition, often described as a limb “falling asleep,” occurs when sustained pressure on a nerve or its neighboring blood vessels causes a temporary inability to transmit signals. For instance, sleeping in an awkward position or carrying a heavy backpack strap that presses directly onto the shoulder can cause this momentary blockage.
The mechanism behind this short-lived numbness is a mild type of nerve injury called neurapraxia. This involves a temporary block in nerve conduction, usually due to compression that affects the nerve’s outer sheath. When the pressure is relieved, the nerve quickly regains its ability to function, which is often perceived as the familiar “pins and needles” sensation. This type of numbness resolves spontaneously and rapidly, typically within minutes of changing position.
Spinal Nerve Compression
When shoulder numbness is chronic or recurrent, the source often traces back to the cervical spine, or the neck, where nerve roots exit the spinal cord. This condition is called cervical radiculopathy, occurring when a nerve root in the neck becomes compressed, irritated, or inflamed. Degenerative changes are a common culprit, as intervertebral discs lose height or joints develop bone spurs (osteophytes), narrowing the space where the nerve exits.
The spinal nerves most frequently associated with shoulder numbness are the C5 and C6 nerve roots, which supply sensation and motor function to the shoulder and upper arm. Compression at the C5 level typically results in numbness or pain concentrated over the shoulder and upper arm, sometimes accompanied by weakness in the deltoid muscle. If the compression is at the C6 level, the numbness may radiate further down the arm and into the thumb side of the hand.
In younger individuals, spinal nerve compression often results from acute trauma that causes a disc to bulge or herniate, pushing against the adjacent nerve root. When the center of the disc is displaced, it can lead to a sharp, burning pain that travels down the arm, a distinguishing feature of radiculopathy. The numbness is often accompanied by muscle weakness in the shoulder or arm, reflecting the compromised motor component of the affected nerve root.
Localized Shoulder and Pathway Issues
Numbness can also originate from issues affecting the nerve pathway after it leaves the spinal column and travels through the neck and shoulder region. The brachial plexus, which supplies the entire arm, is vulnerable to injury or compression in this area. Trauma, such as a fall or a severe shoulder dislocation, can cause stretching or tearing injuries to these nerves, resulting in numbness and significant muscle weakness.
Another cause of pathway-related numbness is Thoracic Outlet Syndrome (TOS), which involves the compression of nerves or blood vessels in the narrow space between the collarbone and the first rib. Neurogenic TOS is the most common form, where the nerves of the lower brachial plexus are compressed. This leads to numbness and tingling that often affects the hand, but can be felt throughout the shoulder and arm. TOS symptoms are frequently made worse by activities that require elevating the arm or placing sustained pressure on the shoulder.
Direct trauma to the shoulder joint, like a humerus fracture or a severe shoulder dislocation, can also cause localized nerve damage. The axillary nerve, which wraps around the head of the humerus, is often injured in such events. Injury to this specific nerve leads to a distinct patch of numbness over the outer, rounded part of the shoulder and difficulty raising the arm sideways.
Duration, Severity, and When to Consult a Doctor
While temporary shoulder numbness is harmless, certain accompanying symptoms require prompt medical evaluation. Numbness that has a sudden onset and is accompanied by severe weakness, paralysis, or a visible deformity suggests an acute, serious injury like a fracture or major nerve trauma. Any numbness following a significant accident or fall should be assessed immediately to rule out serious spinal or plexus damage.
Persistent numbness that does not resolve within a few hours or days, or symptoms that progressively worsen, also warrant a professional examination. These ongoing symptoms may indicate a condition like cervical radiculopathy or Thoracic Outlet Syndrome that requires intervention to prevent further nerve damage. The development of numbness alongside bowel or bladder control issues is a rare but urgent situation that demands immediate emergency attention.