Pain indicates something is wrong. There are at least 250 diseases and disorders including temporomandibular disorders, which have head pain as a symptom. The diagnosis of the disease causing the headache is a very complex task. All pain symptoms are subjective, cannot be precisely measured and largely depend on the patient's ability to describe them. There is much inter-patient variability and symptom overlap.
Psychological factors can exacerbate symptoms and confound diagnoses.
The pathology may be an effect rather than the cause. Shared neurological circuitry in the head and neck often makes the disease identification difficult. The location of the pain may not be the site of the real problem. Intensity and quality of the pain may not relate to the severity of the disease. Multiple diseases or disorders may be present simultaneously.