Common causes of left-sided neck pain are:
- Inflammation. This is the body’s response to injury or infection. It can cause pain, swelling, stiffness, numbness, and other symptoms.
- Muscle strain. If you spend hours leaning forward at your computer, cradling a phone between your right ear and your shoulder, or otherwise stressing your neck muscles, you can end up with pain on the left side of your neck.
- Pinched nerve. A pinched nerve (cervical radiculopathy) occurs when a nerve in the neck becomes irritated or squeezed as it branches out from the spinal cord. If it’s on the left side, it may also cause numbness and pain in the left shoulder.
- Whiplash. You can get whiplash when your head is forcefully thrust back and forth. This can happen from a football tackle, a vehicle accident, or a similar violent incident.
- Acute torticollis. Acute torticollis occurs when the muscles in your neck suddenly contract, causing your head to twist to one side. https://www.nhs.uk/conditions/neck-pain-and-stiff-neck/