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.

    我们都知道头痛是什么感觉。它们常常坏我们的好事，把最美妙的时刻搞得像折磨一般痛苦不堪。据统计，4/5的人患有紧张性头痛，1/7的人则有过偏头痛。每年，因为头痛请假而造成的经济损失高达约15亿英镑。麻烦的是，尽管部分头痛的原因显而易见，另一部分头痛却连名称都难以叫出。而且，你怎能辨别哪些头痛严重、哪些头痛不严重呢？要了解这些，一个好的出发点是先来看看你患的究竟是什么类型的头痛。

    紧张性头痛

    患了紧张性头痛，感觉像脑袋周围无法放松，有一圈压力压着似的。这种头痛的持续时间少则半小时，多则一个星期。紧张性头痛可谓最常见的一种头痛类型，大部分人都有过此种经历。它们的诱发原因，可能和压力有关，也可能由颈部或脸部的肌肉出现问题引起，但原因往往都不明显。大多数人只会偶尔患患紧张性头痛，只有占人口总数3% 的少数人与紧张性头痛常相伴随，平均每两天就被它们侵袭一次。治疗该种头痛，布洛芬缓释胶囊和扑热息痛都是较为有效的药物，此外，锻炼也有所助益。经常性的头痛还可通过阿米替林预防。虽然阿米替林更常被唤作"抗抑郁剂",它却并不能使你开心来达到预防头痛的目的。它的具体工作原理还有待研究。

    偏头痛

    偏头痛会造成头的一侧周期性头痛，持续时长可达4个多小时。偏头痛时，人们往往感到身体不适，坐在一间昏暗的屋子里则会感觉好些。约有1/3到1/4的偏头痛患者在头痛来临之前便有所"预感".这可不是说患者身体周围会发出超自然的光晕，而是说患者会有针刺、钉刺之类的异样感，会注意到明亮的光源，或者感觉与周围人生疏了老远。

    最新一项调查发现，在跟偏头痛患者一起工作的人中，约有1/3的人怀疑患者拿偏头痛作为逃避工作的理由。我们或许该更富同情心些：因为发作一天的严重偏头痛，已被世卫组织并列为与四肢瘫痪、精神变态以及痴呆相同程度的大病。偏头痛并非心理疾病："（而是）明显的脑袋功能紊乱。"伦敦国家神经与外科医院头痛研究组的神经学专科医生，保罗。 沙纳罕（Paul Shanahan）如此解释道。"急性偏头痛发作时，大脑某些区域的活动会有所改变，这样引起的不仅仅是疼痛，还有一系列其它症状。所以偏头痛并不只是 '头痛',更别提是心理疾病了。"

    偏头痛到底由什么样的原因引发？--这个话题多年来被反复地讨论着。过去，研究人员认为，患者的"预感"是由大脑中的血管收缩所造成。血管随后又扩张，从而引发了偏头痛。然而，最新的调查却表明，血液流动的变化也只是脑部活动异常的一个结果，并非构成偏头痛的起始原因。"预感"来临时，大脑表层上的一组脑电波（a wave of electrical activity）传速减慢（速度仅为每分钟几毫米）,由此可引发一系列症状，包括视觉紊乱、针刺或钉刺感、说话吃力以及肢体虚弱等。大脑处理感觉的功能出现障碍，导致患者对动作、光线、声音甚至气味等都格外敏感、难以忍受。

    避开诱因能对缓解偏头痛起到不错的作用，因此，时常写写头痛日记是大有裨益的。然而，仅有20%的偏头痛患者的诱因来自于食物。英国头痛研究协会（British Association for the Study of Headache ,简称Bash）在指导准则中警告说，"太过努力要找出偏头痛的诱因，可能引起患者内省，对治疗不利。"如果非处方药如布洛芬缓释胶囊等无法减轻偏头痛，那么可试试曲坦类药物，或有所帮助。曲坦类药物可通过模拟神经末梢的神经递质复合胺（neurotransmitter serotonin ）来尽量减少痛苦。

    集束性头痛

    集束性头痛可在患者的一只眼附近引起强烈的悸痛感。每次头痛可长达4小时，并伴有红眼、流泪和流涕等症状。

    此种头痛发作起来，可谓头痛欲裂。"集束性头痛据说是人类可能承受的最剧烈的痛苦，"保罗。沙纳罕说，"有时候，患者还因忍受不了这种剧烈、不间断的痛苦，而结束自己的生命。因此集束性头痛又被称为'自杀性头痛'."

    集束性头痛之所以得此名，源于它们倾向于阶段性发作，常常在一天的同一时间来临。"它们的循环周期可能持续几周，几月甚至几年。这显示出'生物钟'也在其中发挥了作用。"沙纳罕说。

    氧气疗法是治疗集束性头痛的最佳方法之（通过面罩，一次性呼吸纯氧20分钟或更长）,并且直到现在依然在投入使用。然而，沙纳罕医生说，有许多人却没能接受到氧气治疗，或者其它有效的治疗方法--如舒马曲坦注射等。"集束性头痛的治疗方法还远未得到推广。因此，很可惜，许多病人因治疗不力，不得不天天承受难以言喻的痛苦。"

    宿醉

    宿醉头痛的确切原因还尚不清楚，但脱不了干系的嫌疑原因倒有一大堆：比如酒精引起脑中血管扩张，对神经末端的复合胺作用产生影响--偏头痛里也会有这两种症状。酒精同样会导致体内缺水--也是一个常常诱发偏头痛的原因。幸运的是，宿醉只要吃点扑热息痛药或睡个好觉便可解决。但部分人可能伴有偏头痛，自己却没意识到，沙纳罕分析说。"如果只要口渴就头痛的话，则很可能患上了偏头痛，同样地，那些喝少量酒便宿醉的人也可能得了偏头痛。此外，酒精还是集束性头痛的强力诱因之一。"

    药物滥用性头痛

    一个悖论是，所有的止痛药，如果长时间服用都可能导致头疼。药物滥用所引起的头痛常常难以同原本的病痛区别开，因此也难以诊断。若有人一月内超过10天服用可待因或曲坦类药物，或者一月内15天服用如扑热息痛或布洛芬等非处方药，那么他就有患上药物滥用性头痛的危险。

    治疗此种头痛的唯一方法是停止服用那些止痛药。停服初期，头痛常常会加剧，直到一个星期或者一个月后才有所好转。

    脑肿瘤

    不超过4%的脑肿瘤患者伴有头痛症状。肿瘤导致头骨内压力增大，引起晨起头痛或者呕吐，且情况逐渐加剧。但只有同时出现脑肿瘤的其他症状，如体重减轻、癫痫、人格改变等，患者才有必要进行脑部扫描。

    蛛网膜下腔出血

    突发性剧烈头痛--疼痛部位往往位于脑后部--可能是由一种叫做蛛网膜下腔出血的脑内出血产生。据许多人描述，这种头痛的感觉，像是被棒球球棒砸上了一记。蛛网膜下腔出血常常由脑底部的一个动脉瘤破裂引起，一旦发作，则需立即检查并治疗。

    颞动脉炎

    年过五旬的人若患上头痛，便可能是由颞动脉炎所致。这种头痛与先前的头痛感觉不同，并可能伴有轻微的头皮脱落或咀嚼疼痛。

    颞动脉炎是由太阳穴内的动脉发炎所引起（所以叫做"颞"动脉炎）,治疗药物为内固醇。该种病痛一旦出现，需及早诊断，否则可能导致双目失明。

    脑膜炎

    头痛时，伴随有高烧、颈僵硬以及（或者）新发皮疹，则可能为脑膜炎。一旦得了脑膜炎，需上医院治疗，越快越好。