Good question coolguy, and one that I’m sure a lot of people want to know the answer to!
The truth is that there are many different causes to headaches, but they can generally be split into three types…
1) Tension headaches are effected by muscle strain on the neck and sometimes even emotional stress – this can also be triggered by eye strain (like staring at a computer screen for too long!)
2) Cluster headaches are a bit of an unknown one – they occur repeatedly over a period of time, but we still don’t know exactly what causes them… it could be to do with blood flow.
3) Finally, migraines… these can be caused by a reduced blood flow to certain areas of your brain, and is thought to be linked to something called serotonin – a neurotransmitter that binds to various receptors in your head 🙂
You know, I had to look this up, because I thought that I knew the answer – but I keep hearing different things, and now I’m confused. When I’m trying to look something up for work (not worth trusting Wikipedia when something is really important), most medical scientists (and anyone working in biomedicine) will turn to an index of scientific articles called Pubmed, which you can get to freely online at: http://www.ncbi.nlm.nih.gov/pubmed/
From here, we can do all sorts of searches for articles that other scientists have published in “peer reviewed” journals. This means that each of the articles has been independently checked by 2-5 experienced scientists with experience in the same field, so it is generally more trustworthy than something we might find on the net. However, it isn’t aimed at the general public, so it can be difficult to follow.
There are many different types of headache, but the commonest is called a “tension-type headache”. The usual source of the pain isn’t in the brain, or the lining of the brain (the meninges), but in the muscles of the head and neck outside the skull. These muscles become tense, often in association with some form of stress, “eye strain”, sleep deprivation or due to many other causes. Despite being very common, the details of how all of this comes about and why it is so sustained, are not very clear at all.
There are other rarer types of headaches, like migraines (where there is a migrating pattern of blood vessel contraction in the linings of the brain) and very severe “thunderclap” headaches due to bleeding into the brain, or “cluster headaches” (related to some problem with a particular nerve in the head called the trigeminal nerve). So, there are lots of different types of headache, but the commonest type of all (tension-type headaches) is the one that least in known about – very frustrating!