What is a headache? Why is it important to know about headache? Headache refers to pain confined to the upper part of the skull, so do not treat jaw pain below the arch of the eyebrow and occipital neck pain below the line of the external occipital ridge as headache; of course, jaw pain and occipital neck pain can radiate and spread to the head, at this time, although it can be called headache, we should still ask carefully about the starting site of pain to help distinguish it from headache, and also help analyze and treat the cause, such as glaucoma with orbital pain first and then to the orbit Frontal pain, cervicogenic headache has pain in the cervical-occipital region first and then spreads to the top of the occipital region. The causes of headache are diverse. Nociceptive endings (i.e., nociceptive receptors) in tissues and structures inside and outside the skull are stimulated by some physical, chemical (including some biochemical) or mechanical stimuli, producing abnormal nerve impulses that are transmitted to the brain via sensory nerves through the corresponding nerve conduction pathways and perceived. Headache is an objective reflection of pain-causing factors in the human body, which is difficult to be perceived by others except for personal experience. The response to headache perception varies greatly between individuals, with some tolerating a certain degree of headache and others having a significant response. Since the distribution of nociceptive receptors in various intracranial tissue structures varies greatly, the sensitivity of various intracranial tissue structures to painful stimuli varies. It follows that the degree of headache is closely related to the size and location of the lesion. Many extracranial pain-causing structures, when stimulated, exhibit not only localized pain but also often widespread diffusion and reflex into the skull. There are many factors that cause headache, and the mechanisms that cause headache are also different. Therefore, we need to understand the knowledge about headache so that we can face headache correctly, neither mistakenly think that there is a tumor in the skull and need to do a CT examination once we have headache, nor should we take headache so seriously that treatment is delayed.