Cluster headache: symptoms, treatment and where oxygen fits

Cluster headache is one of the most severe pain conditions a person can live with, and one of the most misunderstood. It is not a bad migraine. It has its own pattern, its own emergency rules and its own first-line treatments, one of which happens to be oxygen.

That last point causes confusion, so this guide separates two very different uses of oxygen: the mask oxygen that UK guidance recommends for attacks, and the pressurised chamber oxygen that a hyperbaric clinic provides. The second is not a cluster headache treatment, and we say so plainly below.

What is a cluster headache?

Cluster headache is a primary headache, which means it is not caused by another underlying condition. NICE Clinical Knowledge Summaries place it in a group called the trigeminal autonomic cephalalgias and describe it as the most common of them: a frequently recurring, localised, short-lasting but severe headache, usually accompanied by what doctors call autonomic symptoms.

Headache specialists recognise two forms:

• Episodic cluster headache. Attacks come in periods lasting from 7 days to one year, separated by pain-free periods of at least 3 months.
• Chronic cluster headache. Attacks continue for one year or longer without remission, or with remission periods shorter than 3 months.

It is rare. A meta-analysis of 16 population studies, cited by NICE CKS, found a lifetime prevalence of 124 per 100,000 adults. Men are affected more often than women, at a ratio of about 3 to 1, although more women are being diagnosed over time. The peak age of onset is 20 to 40.

What does a cluster headache feel like?

The NHS describes a sharp, burning or piercing pain, usually on one side of the head and around the eye. Typical features include:

• attacks lasting between 15 minutes and 3 hours
• headaches that start and stop quickly, without warning
• several attacks a day, continuing for weeks or months
• attacks at the same time of year or at set times of the day
• pain that makes you restless, so you may want to walk around or move your body
• a drooping, swollen eyelid or a smaller pupil on the same side as the pain

Nobody yet knows what causes cluster headache. Some people notice triggers, and the NHS lists smoking, drinking alcohol, perfume, the smell of paint, nail varnish or petrol, and exercise. A headache diary can help you and your GP spot a pattern.

How is cluster headache different from migraine?

The two can be confused, and only a clinician can make the diagnosis. The Cochrane reviewers who studied oxygen for both conditions summarised the usual differences:

• Associated symptoms. Nausea, vomiting and sensitivity to light are common with migraine, while cluster headache is typically accompanied by tearing and nasal congestion.
• Pattern. Cluster headaches typically occur daily for up to several weeks before resolving, often for lengthy periods.
• Location and character. Cluster pain sits around one eye, on one side. Migraine can affect both sides and is often described as throbbing.

Behaviour during an attack is another clue. The NHS notes that cluster headache pain can make people restless and agitated.

The distinction matters because several medicines that are reasonable for migraine are not recommended for cluster attacks, as the next section explains.

What is the treatment for cluster headache in the UK?

The NICE headache guideline (CG150) recommends offering oxygen, a subcutaneous or nasal triptan, or both, for the acute treatment of cluster headache. It advises against paracetamol, NSAIDs, opioids, ergots or oral triptans for attacks. NICE CKS notes that oral triptans have too slow an onset of action for cluster headache.

Oxygen. NICE specifies 100% oxygen at a flow rate of at least 12 litres per minute, through a non-rebreathing mask with a reservoir bag, with home and ambulatory oxygen arranged. NICE CKS adds practical detail: 12 to 15 litres per minute for 15 to 20 minutes, taking fire hazards into account. Oxygen can be repeated as many times as needed and may be used alongside a triptan. Home oxygen can be provided through the Home Oxygen Order Form (HOOF).

Triptans. CKS notes that the British Association for the Study of Headache guideline describes a subcutaneous sumatriptan injection as the most effective acute treatment, which should provide significant relief within 15 minutes. Nasal sumatriptan or zolmitriptan are alternatives.

Prevention. NICE advises considering verapamil for preventive treatment during a bout. If the prescriber is unfamiliar with its use for cluster headache, they should seek specialist advice first, including advice on ECG monitoring of the heart. This is an off-label use. If verapamil is not tolerated or does not help, a specialist may recommend alternatives such as lithium or topiramate. The NHS also lists corticosteroids among preventive options.

There are no specific tests that diagnose cluster headache. A GP may refer you to a specialist for a brain scan to rule out other causes of similar symptoms.

Is hyperbaric oxygen therapy the same as oxygen for cluster headache?

No. This is the most important distinction on this page.

Normobaric oxygen means breathing high-flow oxygen through a mask at normal air pressure. It is what NICE recommends, it can be kept at home, and it can be started within minutes of an attack beginning.

Hyperbaric oxygen therapy (HBOT) means breathing oxygen inside a pressurised chamber. You can read how it works in what HBOT is. It is delivered in scheduled sessions at a clinic, which makes it impractical for attacks that last 15 minutes to 3 hours and arrive without warning.

The best summary of the research is a 2015 Cochrane review of 11 randomised trials with 363 participants across migraine and cluster headache. For cluster headache it found:

• Mask oxygen. Three trials, with 145 participants, compared normobaric oxygen with sham treatment or ergotamine. A single small study found it effective at ending attacks compared with sham.
• Hyperbaric oxygen. Only two trials, with 29 participants in total, tested HBOT. Both used 2.5 ATA, one for 30 minutes on a single occasion and one for 70 minutes on two consecutive days. The reviewers found no evidence that HBOT was effective for ending cluster attacks. Their plain language summary goes no further than saying HBOT possibly relieves cluster headache pain, based on low quality evidence.
• Prevention. They found no evidence that either form of oxygen can prevent future attacks.

The authors wrote that normobaric oxygen "is cheap, safe, and easy to apply", while the cost and poor availability of HBOT mean further research should focus on people who do not respond to standard therapy.

Does HBOT Medics treat cluster headache?

No. We do not offer hyperbaric oxygen as a treatment for cluster headache, whether to end attacks or to prevent bouts.

Our chamber runs at 1.5 ATA. The only cluster headache trials of HBOT used 2.5 ATA and still did not show a clear benefit, so there is no research result to carry over to a lower-pressure service. If you live with cluster headache, the evidence points to mask oxygen and the medicines above, managed by your GP and a headache specialist.

If you have cluster headache and are considering HBOT for a different reason, list your diagnosis and every medicine, including any preventive treatment, on the medical declaration. Our safety guide explains which conditions and treatments need individual review before pressure exposure. No referral needed. Medical consultation included.

When should you get urgent help for a headache?

Follow the NHS advice rather than waiting to see whether a pattern settles:

• See a GP if you think you might have cluster headaches, your headaches keep coming back, painkillers such as ibuprofen and paracetamol do not help, the pain makes you restless and agitated, or diagnosed cluster headaches are getting worse, lasting longer or no longer responding to your usual treatment.
• Get an urgent GP appointment or call 111 if you have a severe headache with jaw pain when eating, blurred or double vision, a sore scalp, or other symptoms such as numbness or weakness in the arms or legs. These can be symptoms of temporal arteritis.
• Call 999 or go to A&E if, for the first time, one eyelid is drooping or the pupil in one eye is smaller than the other, even if you have already been diagnosed with cluster headaches.

If you want to understand hyperbaric oxygen for other reasons, start with our plain guide to hyperbaric oxygen therapy. For cluster headache itself, the right first conversation is with your GP.