Headache

A headache, or cephalalgia, is a common symptom characterised by pain located in the head, face or neck. It represents one of the most frequently experienced forms of physical discomfort and can arise from a wide range of physiological, environmental or pathological factors. Headaches vary greatly in their severity, duration, pattern and underlying mechanisms. They may present independently—as primary headache disorders—or occur as manifestations of other medical conditions, in which case they are classified as secondary headaches.
Globally, headaches impose a significant burden on public health. Around half of all adults experience at least one headache each year, with tension-type headaches and migraines accounting for the majority of reported cases. Severe or chronic headaches are associated with increased risk of depression and reduced quality of life.

Classification and Epidemiology

More than 200 types of headaches have been described. The International Headache Society’s classification remains the most widely adopted framework, distinguishing between primary and secondary headache disorders.

• Primary headaches are not caused by structural disease or other underlying medical conditions. They include migraines, tension-type headaches and cluster headaches, which collectively account for about 90 per cent of all headache cases. These typically begin between the ages of 20 and 40.
• Secondary headaches result from identifiable causes such as infection, vascular disorders, head injury, adverse effects of medication, or intracranial pathology. Although some secondary headaches are benign, others may indicate serious or life-threatening conditions.

Tension-type headaches affect roughly 2.18 billion people worldwide, making them the most prevalent type. Migraines affect around 848 million individuals and often lead to substantial disability.

Causes and Risk Factors

Headaches can arise from numerous triggers. Common causes include:

• Dehydration, fatigue and sleep deprivation
• Stress-related physiological responses
• Viral infections
• Exposure to loud noises
• Head or neck injuries
• Rapid consumption of cold foods or beverages
• Sinus or dental problems, including sinusitis
• Medication overuse, leading to rebound or painkiller-induced headaches
• Withdrawal from recreational drugs or caffeine

Secondary headaches may indicate systemic infections, vascular abnormalities, gastrointestinal diseases, or other underlying medical issues. Red-flag symptoms—such as sudden severe onset, neurological deficits or fever—may necessitate urgent diagnostic evaluation.

Primary Headache Disorders

Primary headaches encompass several notable forms:

• MigrainesCharacterised by pulsating pain, often unilateral, accompanied by nausea, photophobia and phonophobia. Some individuals experience an aura involving visual or sensory disturbances. Migraines stem from neurological dysfunction rather than vascular dilation and have been linked to abnormal brain signalling pathways.
• Tension-type headachesPresent as bilateral, non-pulsating, “band-like” pressure without significant associated symptoms. They may be episodic or chronic.
• Cluster headachesSevere unilateral pain episodes lasting between 15 and 180 minutes, often centred around the eye. They may present with tearing, nasal congestion and restlessness, occurring in predictable daily cycles. Treatments include triptans, while preventative options range from corticosteroids to lithium.
• Other primary headachesRare forms include:
  • Occipital neuralgia – shooting pain in the face or skull base
  • Hemicrania continua – constant unilateral pain relieved by indometacin
  • Ice-pick headaches – brief, stabbing pains
  • Primary cough headache – triggered by coughing or straining
  • Primary exertional headache – arising during or after exercise
  • Sex-related headaches – occurring before or during orgasm
  • Hypnic headache – nocturnal headaches seen mainly in older adults

Although usually benign, some of these types require exclusion of serious secondary causes before diagnosis.

Secondary Headaches and Serious Causes

Secondary headaches arise due to structural or systemic disease. Important categories include:

• Meningitis or meningoencephalitis, often with fever and neck stiffness
• Intracranial haemorrhage, such as subarachnoid bleeding
• Brain tumours, which may cause worsening pain with exertion or position changes
• Giant-cell arteritis, common in older individuals and associated with tender temporal arteries
• Acute glaucoma, presenting with eye pain, visual changes and nausea
• Postictal headaches following seizures
• Gastrointestinal-related headaches, linked to coeliac disease, H. pylori infection and irritable bowel disorders
• Migraine-associated cyclic vomiting syndrome, which shares neurological features with migraine attacks

Medication overuse headache is a frequent secondary cause in people who take analgesics excessively.

Pathophysiology

Although the brain parenchyma itself lacks pain receptors, many surrounding structures can generate nociceptive signals. These include:

• Extracranial arteries
• The middle meningeal artery
• Large veins and venous sinuses
• Cranial and spinal nerves
• Head and neck muscles
• The meninges, especially the dura mater
• Ocular, dental and oral tissues

Pain is typically triggered by traction, inflammation, dilation or irritation of these structures. Once nociceptors are activated, signals travel along sensory nerve fibres to pain-processing centres in the brain.
The mechanisms underlying primary headaches remain less fully understood. Contemporary research attributes migraines to neural dysfunction, including altered neurotransmitter activity and changes in brainstem–trigeminal pathways. Older vascular theories that implicated dilation of extracranial vessels are no longer considered adequate explanations.
Cluster headaches have been associated with hypothalamic dysfunction affecting circadian rhythms, while tension-type headaches are thought to involve muscular and stress-related mechanisms.

Diagnosis and Management

Diagnosis depends heavily on clinical history and neurological examination. Additional tests—such as imaging or lumbar puncture—are recommended when red flags suggest secondary causes.
Treatment is guided by the underlying type:

• Analgesics such as paracetamol or non-steroidal anti-inflammatory drugs for mild cases
• Triptans, ergot derivatives or preventive agents (e.g., beta-blockers, anticonvulsants) for migraines
• Oxygen therapy or triptans for cluster headaches
• Indometacin for hemicrania continua or certain primary exertional headaches
• Lifestyle modifications, such as hydration, sleep hygiene and stress reduction
• Management of underlying disease for secondary headaches