Brain tissue itself lacks pain-sensitive nerves and does not feel pain. Headaches occur when pain-sensitive nerve endings called nociceptors react to headache triggers (such as stress, certain foods or odors, or use of medicines) and send messages through the trigeminal nerve to the thalamus, the brain's "relay station" for pain sensation from all over the body. The thalamus controls the body's sensitivity to light and noise and sends messages to parts of the brain that manage awareness of pain and emotional response to it.

Other parts of the brain may also be part of the process, causing nausea, vomiting, diarrhea, trouble concentrating, and other neurological symptoms. There are multiple types of headache. Identifying the type prompts proper treatment.

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