Muscle Strain: This is often the most common cause of neck tenderness, resulting from overuse, poor posture, or direct injury to the muscles in the neck. The tenderness is usually localized to the area of strain and can be accompanied by limited range of motion.

Cervical Lymphadenitis: Inflammation of the lymph nodes in the neck, often due to a viral or bacterial infection, can cause tenderness, especially if the nodes become enlarged or suppurative.
Torticollis: A condition characterized by a twisted neck, where the head becomes persistently turned to one side. It can cause significant tenderness and discomfort on the affected side.
Cervical Spondylosis: Wear and tear on the discs and joints in the neck can lead to pain and tenderness, particularly on one side if the degeneration is asymmetric.

Carotid Artery Dissection: A tear in the wall of the carotid artery, which can lead to a stroke. It often presents with sudden onset of neck pain or tenderness, sometimes accompanied by neurological symptoms.
Epidural Abscess: A collection of pus in the space surrounding the spinal cord, which is a medical emergency requiring prompt treatment. Symptoms can include severe neck pain, fever, and neurological deficits.
Lymphoma: Although less common, lymphoma can cause lymph node enlargement and tenderness in the neck. Given its potential severity, it should not be missed.

Branchial Cleft Cyst: A congenital anomaly that can become infected and present as a tender mass in the neck.
Parotid Gland Pathology: Conditions affecting the parotid gland, such as parotitis or a parotid tumor, can cause tenderness in the upper neck.
Osteomyelitis of the Cervical Spine: A rare infection of the bone in the cervical spine, which can cause severe neck pain and tenderness, often accompanied by systemic signs of infection.