We all know what it's like to have a headache. They can turn the best of occasions into a form of torture. Four out of five people get tension headaches. One in seven experience migraines. Headaches cost the economy around ￡1.5bn a year through lost work days. Trouble is, while some causes of headaches are obvious – such as when you've had too many glasses of wine the night before – others are more tricky to call. And how can you tell what's serious and what isn't? A good starting point is knowing what type of headache you have.

    Tension headache

    Tension headaches tend to feel like a pressure or tightness around the head. They can last for only half an hour or up to a week. This is the most common type of headache and most people will have had one. Tension headaches can be stress-related or due to problems with the muscles in the neck and face, but there is often no obvious cause. Most people who get tension headaches don't get them very often but around 3% of the population get them regularly, on average every other day. Ibuprofen or paracetamol are usually effective, and exercise helps too. For regular headaches preventative treatment with amitriptyline is available. Although better known as an antidepressant, amitriptyline doesn't prevent headaches by making you happier, although why exactly it does work is still not known.

    Migraine

    Migraine causes recurrent headaches on one side of the head that last for more than four hours. It is common to feel sick and sitting in a dark room often helps. A quarter to a third of migraine sufferers get an "aura" before the headache begins. This is not a supernatural glow around the body, but unusual sensations such as pins and needles, seeing bright lights, or feeling distant from people around you.

    A recent survey found that a third of people who work with a migraine sufferer are suspicious that migraine is used as an excuse for days off work. Perhaps we should be more sympathetic: the World Health Organisation has ranked a day with severe migraine as disabling as a day with quadriplegia, psychosis or dementia. It is not a psychological illness: "Migraine is very clearly a brain disorder," says Dr Paul Shanahan, consultant neurologist at the Headache Group, National Hospital for Neurology and Neurosurgery in London. "There are changes in activity of certain brain regions which occur during an acute migraine attack that give rise not just to pain, but a wide variety of symptoms. It's not 'just a headache', and it's certainly not psychological."

    The mechanism underlying a migraine has been the subject of much debate over the years. Researchers used to think that the aura was caused by blood vessels in the brain narrowing. Then the vessels widen, which was thought to cause the headache. However, more recent research shows that blood flow changes may be a consequence of unusual brain activity rather than the initial cause of the migraine. During an aura, a wave of electrical activity travels slowly （at only a few millimetres per minute） across the surface of the brain. This can trigger a variety of symptoms including visual disturbance, pins and needles, speech difficulties and limb weakness. The way the brain processes sensations becomes disordered so that movement, lights, sounds and even smells become harder to tolerate.

    Avoiding triggers can be useful so keeping a headache diary can help. However, only 20% of migraine sufferers have a dietary trigger. The British Association for the Study of Headache （Bash） guidelines warn that "too much effort in seeking triggers causes introspection and may be counter-productive." If migraine can't be relieved by over-the-counter painkillers such as ibuprofen, triptans can help. Triptans can abort migraine attacks by mimicking the effect of the neurotransmitter serotonin at nerve receptors.

    Cluster headache

    Cluster headaches cause severe throbbing pain on one side of the face around the eye. Each headache lasts for up to four hours and is often accompanied by a red eye, tears and a runny nose.

    The pain can be unbearable. "Cluster headaches have been described as the most severe form of pain a human can experience," says Shanahan. "Occasionally patients can be driven to suicide by the severity and relentlessness of the pain, hence their description as 'suicide headaches'."

    The name derives from their tendency to occur in clusters, often occurring at the same times every day. "These cycles can run for weeks, months or even years, and point to the brain's 'body clock' as having a role in the condition," says Shanahan.

    Oxygen therapy （breathing pure oxygen through a mask for 20 minutes or more） is one of the best treatments for cluster headache and is available on prescription. However, not enough people are getting this, or other effective treatments such as sumatriptan injections, according to Shanahan. "These treatments for cluster headache are under-utilised, and, frustratingly, we see patients who are undertreated while having excruciating daily pain."

    Hangover

    The exact cause of a hangover headache isn't known but there are plenty of likely culprits: alcohol causes blood vessels in the brain to widen and can alter the effects of serotonin on nerve endings – both of which occur in migraine. Alcohol also causes dehydration, a common trigger of migraine attacks. Fortunately the pain usually goes after some paracetamol and a good night's sleep but some may have migraine without realising it, according to Shanahan. "People who get headaches when thirsty may well have migraine, as do many people who get bad hangovers after fairly modest amounts of alcohol. Alcohol is often a very potent trigger for cluster headache, as well."

    Medication overuse headache

    Paradoxically, all painkillers can cause a headache if taken regularly over a long period of time. Medication overuse headache is difficult to tell apart from the original headache so it can be very difficult to diagnose. Anyone who takes codeine or triptan-based drugs for more than 10 days a month or other over-the-counter remedies such as paracetamol or ibuprofen for 15 days a month is at risk.

    The only treatment is to stop taking the painkillers. The headache often gets worse initially, and improvement may only be seen between a week and a month later.

    Brain tumour

    Fewer than 4% of brain tumours present with a headache. Tumours cause the pressure within the skull to rise, which causes a morning headache and vomiting that gradually gets worse. Brain scans are only necessary when these or other features of a tumour such as weight loss, seizures or personality change are present.

    Subarachnoid haemorrhage

    A sudden severe headache, usually at the back of the head, may be caused by a bleed inside the brain called a subarachnoid haemorrhage. Many people with this say it's like being hit with a baseball bat. It is commonly caused by the rupture of an aneurysm at the base of the brain and needs urgent investigation and treatment.

    Temporal arteritis

    Headaches in people over 50 can be due to temporal arteritis. It often feels different to previous headaches and can be accompanied by a tender scalp or pain when chewing.

    Temporal arteritis is caused by inflammation of the artery in the temple （hence "temporal"） and can be treated with steroids. It is important to diagnose early as it can lead to blindness if untreated.

    Meningitis

    A headache with a high temperature, neck stiffness and/or a new rash may be due to meningitis. This needs hospital treatment as soon as possible.

    我們都知道頭痛是什么感覺。它們常常壞我們的好事，把最美妙的時刻搞得像折磨一般痛苦不堪。據統計，4/5的人患有緊張性頭痛，1/7的人則有過偏頭痛。每年，因為頭痛請假而造成的經濟損失高達約15億英鎊。麻煩的是，盡管部分頭痛的原因顯而易見，另一部分頭痛卻連名稱都難以叫出。而且，你怎能辨別哪些頭痛嚴重、哪些頭痛不嚴重呢？要了解這些，一個好的出發點是先來看看你患的究竟是什么類型的頭痛。

    緊張性頭痛

    患了緊張性頭痛，感覺像腦袋周圍無法放松，有一圈壓力壓著似的。這種頭痛的持續時間少則半小時，多則一個星期。緊張性頭痛可謂最常見的一種頭痛類型，大部分人都有過此種經歷。它們的誘發原因，可能和壓力有關，也可能由頸部或臉部的肌肉出現問題引起，但原因往往都不明顯。大多數人只會偶爾患患緊張性頭痛，只有占人口總數3% 的少數人與緊張性頭痛常相伴隨，平均每兩天就被它們侵襲一次。治療該種頭痛，布洛芬緩釋膠囊和撲熱息痛都是較為有效的藥物，此外，鍛煉也有所助益。經常性的頭痛還可通過阿米替林預防。雖然阿米替林更常被喚作"抗抑郁劑",它卻并不能使你開心來達到預防頭痛的目的。它的具體工作原理還有待研究。

    偏頭痛

    偏頭痛會造成頭的一側周期性頭痛，持續時長可達4個多小時。偏頭痛時，人們往往感到身體不適，坐在一間昏暗的屋子里則會感覺好些。約有1/3到1/4的偏頭痛患者在頭痛來臨之前便有所"預感".這可不是說患者身體周圍會發出超自然的光暈，而是說患者會有針刺、釘刺之類的異樣感，會注意到明亮的光源，或者感覺與周圍人生疏了老遠。

    最新一項調查發現，在跟偏頭痛患者一起工作的人中，約有1/3的人懷疑患者拿偏頭痛作為逃避工作的理由。我們或許該更富同情心些：因為發作一天的嚴重偏頭痛，已被世衛組織并列為與四肢癱瘓、精神變態以及癡呆相同程度的大病。偏頭痛并非心理疾病："（而是）明顯的腦袋功能紊亂。"倫敦國家神經與外科醫院頭痛研究組的神經學專科醫生，保羅。 沙納罕（Paul Shanahan）如此解釋道。"急性偏頭痛發作時，大腦某些區域的活動會有所改變，這樣引起的不僅僅是疼痛，還有一系列其它癥狀。所以偏頭痛并不只是 '頭痛',更別提是心理疾病了。"

    偏頭痛到底由什么樣的原因引發？--這個話題多年來被反復地討論著。過去，研究人員認為，患者的"預感"是由大腦中的血管收縮所造成。血管隨后又擴張，從而引發了偏頭痛。然而，最新的調查卻表明，血液流動的變化也只是腦部活動異常的一個結果，并非構成偏頭痛的起始原因。"預感"來臨時，大腦表層上的一組腦電波（a wave of electrical activity）傳速減慢（速度僅為每分鐘幾毫米）,由此可引發一系列癥狀，包括視覺紊亂、針刺或釘刺感、說話吃力以及肢體虛弱等。大腦處理感覺的功能出現障礙，導致患者對動作、光線、聲音甚至氣味等都格外敏感、難以忍受。

    避開誘因能對緩解偏頭痛起到不錯的作用，因此，時常寫寫頭痛日記是大有裨益的。然而，僅有20%的偏頭痛患者的誘因來自于食物。英國頭痛研究協會（British Association for the Study of Headache ,簡稱Bash）在指導準則中警告說，"太過努力要找出偏頭痛的誘因，可能引起患者內省，對治療不利。"如果非處方藥如布洛芬緩釋膠囊等無法減輕偏頭痛，那么可試試曲坦類藥物，或有所幫助。曲坦類藥物可通過模擬神經末梢的神經遞質復合胺（neurotransmitter serotonin ）來盡量減少痛苦。

    集束性頭痛

    集束性頭痛可在患者的一只眼附近引起強烈的悸痛感。每次頭痛可長達4小時，并伴有紅眼、流淚和流涕等癥狀。

    此種頭痛發作起來，可謂頭痛欲裂。"集束性頭痛據說是人類可能承受的最劇烈的痛苦，"保羅。沙納罕說，"有時候，患者還因忍受不了這種劇烈、不間斷的痛苦，而結束自己的生命。因此集束性頭痛又被稱為'自殺性頭痛'."

    集束性頭痛之所以得此名，源于它們傾向于階段性發作，常常在一天的同一時間來臨。"它們的循環周期可能持續幾周，幾月甚至幾年。這顯示出'生物鐘'也在其中發揮了作用。"沙納罕說。

    氧氣療法是治療集束性頭痛的最佳方法之（通過面罩，一次性呼吸純氧20分鐘或更長）,并且直到現在依然在投入使用。然而，沙納罕醫生說，有許多人卻沒能接受到氧氣治療，或者其它有效的治療方法--如舒馬曲坦注射等。"集束性頭痛的治療方法還遠未得到推廣。因此，很可惜，許多病人因治療不力，不得不天天承受難以言喻的痛苦。"

    宿醉

    宿醉頭痛的確切原因還尚不清楚，但脫不了干系的嫌疑原因倒有一大堆：比如酒精引起腦中血管擴張，對神經末端的復合胺作用產生影響--偏頭痛里也會有這兩種癥狀。酒精同樣會導致體內缺水--也是一個常常誘發偏頭痛的原因。幸運的是，宿醉只要吃點撲熱息痛藥或睡個好覺便可解決。但部分人可能伴有偏頭痛，自己卻沒意識到，沙納罕分析說。"如果只要口渴就頭痛的話，則很可能患上了偏頭痛，同樣地，那些喝少量酒便宿醉的人也可能得了偏頭痛。此外，酒精還是集束性頭痛的強力誘因之一。"

    藥物濫用性頭痛

    一個悖論是，所有的止痛藥，如果長時間服用都可能導致頭疼。藥物濫用所引起的頭痛常常難以同原本的病痛區別開，因此也難以診斷。若有人一月內超過10天服用可待因或曲坦類藥物，或者一月內15天服用如撲熱息痛或布洛芬等非處方藥，那么他就有患上藥物濫用性頭痛的危險。

    治療此種頭痛的唯一方法是停止服用那些止痛藥。停服初期，頭痛常常會加劇，直到一個星期或者一個月后才有所好轉。

    腦腫瘤

    不超過4%的腦腫瘤患者伴有頭痛癥狀。腫瘤導致頭骨內壓力增大，引起晨起頭痛或者嘔吐，且情況逐漸加劇。但只有同時出現腦腫瘤的其他癥狀，如體重減輕、癲癇、人格改變等，患者才有必要進行腦部掃描。

    蛛網膜下腔出血

    突發性劇烈頭痛--疼痛部位往往位于腦后部--可能是由一種叫做蛛網膜下腔出血的腦內出血產生。據許多人描述，這種頭痛的感覺，像是被棒球球棒砸上了一記。蛛網膜下腔出血常常由腦底部的一個動脈瘤破裂引起，一旦發作，則需立即檢查并治療。

    顳動脈炎

    年過五旬的人若患上頭痛，便可能是由顳動脈炎所致。這種頭痛與先前的頭痛感覺不同，并可能伴有輕微的頭皮脫落或咀嚼疼痛。

    顳動脈炎是由太陽穴內的動脈發炎所引起（所以叫做"顳"動脈炎）,治療藥物為內固醇。該種病痛一旦出現，需及早診斷，否則可能導致雙目失明。

    腦膜炎

    頭痛時，伴隨有高燒、頸僵硬以及（或者）新發皮疹，則可能為腦膜炎。一旦得了腦膜炎，需上醫院治療，越快越好。