 to nerves in the skull where it activates pain and inflammatory receptors causing headaches. Now, you remember the brain has no pain receptors. The sensation of headaches comes from areas outside the brain that are in the peripheral nervous system. But how the brain, which is not directly linked to the peripheral nervous system, as this article says, and I argue with that, triggers nerves to cause headaches, which makes them difficult to heal. Yeah, because you're going after it chemically.