Severe Headache: Causes, Red Flags, Diagnosis and When to Seek Urgent Care

Headache is one of the most common symptoms people experience, and the vast majority are caused by benign, self-limiting conditions such as tension headache or migraine. However, a small proportion of headaches — particularly those that are sudden, unusually severe, or accompanied by certain warning signs — can indicate a serious underlying problem such as bleeding around the brain, infection, or stroke.

This guide is written for anyone experiencing a severe or unusual headache, or caring for someone who is. It explains the difference between common, non-urgent headache types and the red-flag features that should prompt immediate emergency assessment, how headaches are typically investigated, and what treatment and prevention options exist.

• "All severe headaches need a brain scan." Most headaches, even severe ones, are diagnosed based on history and examination alone; imaging is reserved for those with red-flag features.
• "Migraines are 'just a bad headache'." Migraine is a distinct neurological condition that can be significantly disabling and often requires specific treatment strategies, not just pain relief.
• "Painkillers always help, so take more if it doesn't work." Frequent use of pain relief (more than 10–15 days a month) can itself cause medication-overuse headache, making headaches worse over time.
• "A headache that responds to rest can't be serious." While reassuring, response to rest alone should not replace assessment when other red-flag features are present.

• Tension headache — bilateral pressure or tightness, often described as a "tight band"; commonly linked to stress, posture, or fatigue.
• Migraine — often one-sided, pulsating or throbbing, with nausea and sensitivity to light and sound; may have a preceding "aura" of visual or sensory changes.
• Cluster headache — severe, one-sided pain around or behind one eye, occurring in clusters over weeks, often with eye redness or a runny nose on the same side.
• Medication-overuse headache — arises from frequent use of pain relief or migraine medication, creating a cycle of worsening headache.
• Sinus headache — pressure around the forehead, cheeks, or eyes, usually linked to sinus congestion or infection.

Diagnosis usually begins with a detailed history — how the headache started, its location, pattern, triggers, and any associated symptoms — along with a neurological examination. Most headaches do not require imaging. When red-flag features are present, doctors may order:

• CT or MRI brain scan — to rule out bleeding, stroke, or a mass. See our guides on CT scan results and how to read an MRI report.
• Blood tests — including inflammatory markers if temporal arteritis is suspected.
• Lumbar puncture — occasionally used if meningitis or subarachnoid haemorrhage is suspected and imaging is inconclusive.

Treatment depends on the headache type. Tension headaches often respond to simple pain relief, hydration, and stress management. Migraine may require specific medications (triptans), anti-nausea medication, and preventive treatments if frequent. Cluster headache often needs specialist treatment, including oxygen therapy for acute attacks. Reducing triggers — such as poor sleep, dehydration, skipped meals, and excessive screen time — can help prevent recurrent headaches. Tracking your sleep patterns may help identify contributing factors.