When a tension-type headache occurs for at least 15 days per month. CTTH can have debilitating effects on patients.

The mechanism by which a tension-type headache becomes chronic is not fully understood. The current understanding is that abnormal input from muscles in the head and neck, and vascular structures, sensitize peripheral nociceptors (pain receptors). This results in the sensitization of second-order neurons in the spinal cord and A-Beta fibers become pro-nociceptive. The PAG reduces inhibition of pain, the RVM of medulla increases facilitation of pain. Ultimately, this causes increased pain signals to the thalamus and then the somatosensory cortex.