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What causes numbness in the left arm and hand?

Medically reviewed by William Ross Perlman, PhD, CMPP on October 15, 2019. Written by Karen Eisenbraun. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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What causes tingling in the left arm? | Inadequate blood flow | Nerve injuries | Hypothyroidism | Herniated disc | Vitamin B12 deficiency | Fractures | Carpal tunnel syndrome | Cubital tunnel syndrome | Diabetic neuropathy | Multiple sclerosis | Stroke | What to do if you experience numbness or tingling in the left arm

Wondering what could be causing the numbness or tingling you’ve been feeling in your left arm?

Numbness and tingling in the left arm can be caused by something as simple as sleeping on your arm, but it may also be a sign of a serious health condition—so keep reading to learn more about the possible causes, from hypothyroidism and vitamin deficiencies to carpal tunnel syndrome and more.


What causes tingling in the left arm?

Several possible factors can cause numbness or a tingling sensation in the left arm, including the following.

Inadequate blood flow

Inadequate blood flow in the body can cause numbness and tingling in both your left and right arms. Restricted blood flow to the arms can result from injuries or from underlying health conditions such as high blood pressure, diabetes, or kidney failure. If inadequate blood flow is causing tingling in your left arm, you may also experience pain, swelling, and cold hands and fingers.

Nerve injuries

Injuries that affect the nerves in your left arm can interrupt messages from your brain and cause numbness. For instance, brachial plexus neuropathy is a type of nerve injury characterized by damage to the nerves that run down the arms from the spinal cord. Brachial plexus neuropathy can cause pain in the shoulders and arms, as well as numbness and limited movement. Contact sports, auto accidents, and other factors can result in this kind of nerve injury.


An underactive thyroid—a condition also known as hypothyroidism—can cause a number of symptoms, including numbness, tingling, and a painful “pins-and-needles” sensation that can affect the arms. Hypothyroidism results from the underproduction of thyroid hormone by the thyroid gland, and can also lead to symptoms like fatigue, cold sensitivity, weight gain, dry skin, and more.

Easily test the 3 main thyroid hormones (plus thyroid antibodies) with the Everlywell at-home Thyroid Test—and conveniently access your results on our secure, online platform.

Herniated disc

A herniated disc located near nerves that run through your left arm may cause your arm to tingle and feel numb. Risk factors associated with this condition include repetitive bending or twisting of the lower back, lifting heavy objects, smoking, and having a physically inactive lifestyle.

Vitamin B12 deficiency

Vitamin B12 is a key nutrient that helps the nervous system function well, so it probably doesn’t come as too much of a surprise that a B12 deficiency can lead to paresthesia—a tingling feeling or numbness that typically affects the arms, hands, legs, or feet.

The recommended dietary allowance for vitamin B12 is 2.4 mcg per day for adult men and non-pregnant women. Vitamin B12 is found in many animal products including fish, poultry, eggs, meat, and milk—and it’s also available as a nutritional supplement for those who need to boost their intake but don’t get enough of this vitamin from dietary sources.


A bone fracture in your arm can cause inflammation, swelling, and pain, and interfere with nearby nerves, causing numbness and tingling. Other symptoms of a fracture in the arm include a misshapen arm, a visibly out-of-place joint, bleeding, a protruding bone, limited mobility in the arm, and the inability to move the arm. If you suspect you have a bone fracture, seek medical attention right away.

Carpal tunnel syndrome

Carpal tunnel syndrome occurs when the median nerve that runs from the forearm to the palm of the hand becomes pinched at the wrist. Tingling and numbness in the arms are common symptoms of carpal tunnel, as well as frequent burning and itching.

Carpal tunnel is more common in women than men, and in those who perform repetitive tasks with their hands and wrists, such as sewing, fishing, and typing. This condition may be treated with surgery, or with non-surgical treatments including splinting and prescription medications.

Cubital tunnel syndrome

Cubital tunnel syndrome results from the pinching of the ulnar nerve, which runs on the inner side of the elbow. This condition can cause numbness, tingling, and pain in the fingers, hand, forearm, and elbow—especially when the elbow is bent for a long period of time (such as during sleep). Treatment options for cubital tunnel syndrome include surgery, elbow braces, and more.

Diabetic neuropathy

Nerve damage caused by diabetes is referred to as diabetic neuropathy. Diabetes is associated with chronically high levels of blood glucose—which can result in nerve damage. Symptoms of diabetic neuropathy will vary from person to person depending on the type of neuropathy they have, but numbness and tingling in the limbs are common symptoms.

Diabetic neuropathy affects more than half of all people who have diabetes—but working closely with one’s care team to manage blood sugar levels may help reduce the risk.

Regular HbA1c testing is a key part of managing diabetes. You can easily check your HbA1c from the comfort of home with our at-home A1c test (which requires only a simple finger prick to collect a small blood sample).

Multiple sclerosis

A tingling and numb left arm may be an early sign of multiple sclerosis (MS). This nervous system disease damages the material that surrounds and protects nerve cells, slowing down or blocking messages between your brain and body. Symptoms of multiple sclerosis include muscle weakness, problems with balance and coordination, cognitive problems, visual disturbances, and numbness and tingling sensations—sometimes affecting only one part of the body.


Stroke is a serious and potentially fatal condition associated with sudden numbness in the face, leg, or arm—often occurring on just one side of the body. A stroke occurs when blood flow to a part of the brain is interrupted, resulting in the death of brain cells. A stroke may lead to symptoms in your left arm if the brain cells controlling that arm are affected. In addition to numbness and tingling, you may also experience sudden confusion, difficulty speaking or understanding speech, difficulty seeing (which can affect one or both eyes), difficulty walking (which can include dizziness, lack of balance, and loss of coordination), and/or a sudden, severe headache.

If you or someone else may be experiencing a stroke, call 9-1-1 immediately so EMS responders can start life-saving treatment before arrival at an emergency room.

What to do if you experience numbness or tingling in the left arm

Make an appointment with your healthcare provider if you’re experiencing numbness and tingling in your left arm. They may perform an examination, provide a proper diagnosis, and treat the root cause of the problem to reduce or eliminate your symptoms.

Seek emergency medical treatment immediately by calling 9-1-1 if your left arm suddenly goes numb, as this is a warning sign of stroke.

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1. Brachial plexus injury. Mayo Clinic. URL. Accessed October 15, 2019.

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3. Chaker L, Bianco AC, Jonklaas J, Peeters RP. Hypothyroidism. Lancet. 2017;390(10101):1550-1562. doi:10.1016/S0140-6736(17)30703-1

4. Herniated disk. MedlinePlus. URL. Accessed October 15, 2019.

5. Kumar N. Neurologic aspects of cobalamin (B12) deficiency. Handb Clin Neurol. 2014;120:915-926. doi:10.1016/B978-0-7020-4087-0.00060-7

6. Update on Vitamin B12 Deficiency. American Family Physician. URL. Accessed October 15, 2019.

7. Paresthesia Information Page. National Institure of Neurological Disorders and Stroke. URL. Accessed October 15, 2019.

8. Institute of Medicine (US) Committee on Multiple Sclerosis: Current Status and Strategies for the Future, Joy JE, Johnston RB Jr., eds. Multiple Sclerosis: Current Status and Strategies for the Future. Washington (DC): National Academies Press (US); 2001.

9. Stroke Signs and Symptoms. Centers for Disease Control and Prevention. URL. Accessed October 15, 2019.

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