What causes pain in the large tendon behind the left ear?

Pain in the large tendon behind the left ear may be caused by conditions such as muscle strain, greater occipital neuralgia, or mastoiditis.

1. Muscle Strain

Prolonged turning of the head to the left or maintaining a static lateral head position without adequate rest may lead to strain of the left cervical muscles, resulting in localized swelling, soreness, or sharp pain in the neck. As pain intensifies, it may radiate, causing pain in the large tendon behind the left ear.

2. Greater Occipital Neuralgia

Infection (e.g., viral), prolonged forward head posture during desk work, improper sitting posture—leading to chronic soft-tissue strain in the neck—or cervical spine pathology may all cause recurrent, paroxysmal, transient pain within the distribution area of the greater occipital nerve, subsequently manifesting as pain in the large tendon behind the left ear.

3. Mastoiditis

Mastoiditis may develop when host immunity is compromised and pathogenic bacteria—such as *Staphylococcus aureus* or *Streptococcus pneumoniae*—invade, or when otitis media is inadequately treated, allowing middle ear inflammation to progress chronically. This condition can result in pain, redness, and swelling behind the left ear, along with headache.