Numbness in the left arm can happen due to musculoskeletal problems, such as poor posture or tendinitis, which may compress nerves and reduce blood flow. However, it can also indicate more serious conditions, including a heart attack, stroke, or problems with circulation.

This numbness often causes decreased sensation in the arm and hand, and may come with other symptoms like chest pain, neck pain, shortness of breath, or muscle cramps. These signs can help healthcare providers determine whether the cause is related to the heart, nerves, or muscles.

Treatment for numbness in the left arm depends on the underlying cause and may include rest, physical therapy, anti-inflammatory medications, or vitamin B12 supplements. In urgent cases, such as heart attack or stroke, immediate medical care is essential to prevent complications and restore proper function.

Why is my left arm numb?

Numbness in the left arm can be caused by:

1. Heart attack

Numbness and tingling in the left arm is one of the main symptoms of a heart attack. A heart attack can also cause other symptoms, like sharp or tight chest pain, general malaise, dry cough, and difficulty breathing. Read more about common symptoms of a heart attack.

A heart attack occurs due to reduced blood flow to the heart, which, in most cases, is caused by a build up of fatty plaque within the blood vessels.

Be sure to learn about what causes a heart attack so that you can prevent one in the future.

What to do: If you suspect your symptoms are related to a heart attack, seek immediate medical attention or call 911. Treatment usually includes oxygen to facilitate breathing and medications that promote blood flow to the heart.

Some patients may require cardiac catheterization, which involves inserting a stent or balloon into the affected vessels to restore blood flow and prevent tissue death.

Following a heart attack, it is important for patients to engage in certain health measures, like regular exercise, smoking cessation, reduced alcohol intake, and a healthy diet that is low in fried foods.

2. Poor posture

Poor posture can play a key role in causing numbness and tingling in the left arm. When the arm and spine are positioned incorrectly, nerves can become compressed, leading to these symptoms.

People who work at a computer are especially at risk for left arm numbness, particularly if their arms lack proper support. Sitting with poor posture or using a chair or desk at the wrong height can also result in numbness.

Jobs that put frequent pressure on the shoulder or arm, such as delivery work or construction, may increase the likelihood of arm numbness. Additionally, sleeping positions and any existing spinal problems can contribute to numbness in the left arm.

What to do: To improve posture and prevent left arm numbness, it is important to maintain a straight back and to distribute weight equally between both feet when standing. When sitting, you should ensure your lower back is supported in a chair and your feet are flat on the ground.

3. Tendinitis

Tendinitis is an inflammation of the tendons, which connect bones to muscle. This inflammation may emerge due to repetitive movements, like doing laundry, cooking, or writing and typing for prolonged periods. These activities are associated with numbness and tingling in the arms due to frequent employment of the arms or elbows.

In addition, people may report arm weakness, difficulty moving and cramping.

What to do: Tendinitis treatment usually involves anti-inflammatory medications, cold compresses 3 times per day for 20 minutes, and physical therapy. You should also avoid heavy lifting and any movements or activities that triggered this condition.

4. Nerve injury or compression

Certain situations may lead to compression of nerves in the back, resulting in numbness and tingling sensations that can radiate to the arms.

Common causes include spinal tumors, osteoarthritis, infections, prolonged periods in one position, or a herniated disc in the neck (cervical disc hernia). These conditions can press on or injure nerves, triggering symptoms in the back, arms, or other areas connected to the affected nerves.

What to do: In these cases, patients are advised to follow up with a neurologist or an orthopedic surgeon to determine the underlying cause of the nerve compression. The doctor will perform a physical assessment and order imaging tests to confirm a diagnosis. Nerve-related conditions are usually treated with physical therapy, although surgery may be needed.

5. Stroke

A stroke, also known as a cerebrovascular accident (CVA), can cause numbness or tingling in the left arm. Other common warning signs of stroke include a severe headache, weakness or paralysis on one side of the body, slurred or garbled speech, and loss of sensation.

What to do: If you notice any stroke symptoms, it is important to call 911 or proceed immediately to the hospital for treatment.

6. Peripheral neuropathy

Peripheral neuropathy is a disease that affects the peripheral nerves, which are located outside of the brain and spinal cord. These nerves coordinate various bodily functions, such as touch sensation, pain, and muscular movements. This condition is often a consequence of diabetes, and is referred to as diabetic neuropathy in these cases.

In addition to arm numbness, peripheral neuropathy can cause other symptoms like pain, burning, cramping, and muscle spasms.

What to do: Treatment for peripheral neuropathy should be done by a neurologist. The goal of treatment is to manage the underlying cause of this condition. Treatment may include medications, physical therapy, and, in some cases, surgery.

7. Poor circulation

Poor circulation occurs when blood cannot flow easily through the blood vessels. This can happen due to fatty plaque buildup in the arteries (atherosclerosis), blood clots, or health issues like diabetes. Poor circulation can also result from physical pressure on the arm, such as sleeping in a position that compresses blood vessels.

In addition to arm numbness, other symptoms may also emerge, like tingling, cold finger tips, pale or blue skin, or swelling.

What to do: Treatment for poor circulation should be managed by a cardiologist, who may prescribe statins, aspirin, warfarin, and/or blood pressure medications (antihypertensives). The type of medications prescribed will depend on the underlying cause of the poor circulation.

8. Vitamin B12 deficiency

Vitamin B12 is a vitamin that is essential for healthy nerve functioning and red blood cell production. Decreased levels in the body that are left untreated can lead to nerve damage in the arms and legs, resulting in numbness.

Other signs of a vitamin B12 deficiency include fatigue, weakness, problems with balance, pallor, and even memory or mood issues. Read more about what causes a vitamin B12 deficiency and how it's diagnosed.

What to do: Vitamin B12 deficiencies can often be treated with supplementation, dietary changes, oral supplements, or B12 injections.

It is also important to identify the underlying cause of a vitamin B12 deficiency, such as whether it is related to low B12 in the diet or decreased B12 absorption in the gut, for example. Once vitamin B12 levels are within normal levels, numbness tends to resolve.

Check out foods that are high in vitamin B12 that you can incorporate into your diet.

9. Anxiety or panic attacks

Anxiety or panic attacks are usually triggered by fear or stress and cause the body’s “fight or flight” response. This activates the sympathetic nervous system and leads to both physical and psychological symptoms.

One common effect is hyperventilation (rapid or deep breathing), which can lower carbon dioxide levels in the blood, increase nerve sensitivity, and cause numbness or tingling in the limbs.

In addition to arm numbness and hyperventilation, anxiety and panic attacks can also cause rapid heart rate, chest tightness, dizziness, and sweating.

What to do: To help relieve numbness in your arm, try slow, deep breathing exercises to help restore oxygen levels in the blood. Grounding exercises and meditation can also be beneficial for reducing anxiety levels in acutely stressful moments, however frequent events should be treated with long-term therapy involving CBT (cognitive behavioral therapy), stress management, and possibly medication.

10. Brachial plexus injury

A brachial plexus injury refers to damage to the web of nerves (the brachial plexus) that come from the spine and innervate the shoulder, arm, and hand. Injuries caused by trauma (e.g. a car accident), contact sports, tumors, or gunshot wounds, for example, can disrupt nerve signals, and cause symptoms like numbness, weakness, and tingling in the affected arm.

What to do: Very severe brachial plexus injuries may require surgical repair, while mild to moderate injuries can be treated with rest, physical therapy, analgesics, and nerve medications. Some patients may also benefit from corticosteroid medications and occupational therapy, especially if numbness persists for weeks to months.

Numbness in Left Arm: Main Causes & What to Do