What Causes Hemicrania Continua? Genetic or Contagious?

Hemicrania continua (HC) is a neurological condition, and its exact underlying cause is still not fully understood ^[1]. However, it is not contagious, meaning you cannot catch it from or pass it to anyone else ^[2]. While rare familial cases exist, no clinically useful inherited risk or genetic pattern has been established, so it is not generally considered a condition you are likely to inherit or pass down to your children ^[3].

Proposed Mechanisms in the Brain

Hemicrania continua belongs to a family of headache disorders known as trigeminal autonomic cephalalgias (TACs) ^[4]. Current medical models suggest the symptoms involve the trigeminal-autonomic reflex, a specific nerve network in the head ^[5]. This reflex helps explain why HC pain is typically strictly on one side of the head and is often accompanied by autonomic symptoms—automatic body responses like a tearing eye, a runny nose, facial sweating, or a drooping eyelid on that same side ^[5].

While there is no single proven cause, researchers have proposed several possibilities:

• Findings in imaging studies: Some functional brain scans have observed increased activity in the hypothalamus (a deep brain structure that helps regulate automatic functions) and the pons (part of the brainstem) during HC episodes ^[5][6].
• Proposed chemical signals: Researchers are also investigating whether neuroinflammation (inflammation of the nerves) and certain chemical messengers in the brain play a role, though this remains a research hypothesis rather than a settled fact ^[7][8].

Is Hemicrania Continua Genetic?

For the vast majority of people, hemicrania continua appears sporadically without a family history ^[3]. A very small number of familial cases have been reported (such as in a mother and daughter), which suggests genetics might play a minor role for some individuals ^[3]. However, there is no genetic test for HC, and it is not established as a hereditary disease ^[3].

Can Hemicrania Continua Be Contagious?

No, hemicrania continua is a neurological condition, not an infectious disease, so it cannot spread from person to person ^[2].

Rarely, prior infections affecting nearby nerves or tissues—such as shingles (herpes zoster) or invasive sinus fungal infections—can cause a secondary headache with some similar features ^[9][2]. However, this is due to localized tissue effects, and the underlying headache disorder is never contagious.

The Importance of Ruling Out “Secondary” Causes

When a doctor diagnoses hemicrania continua, they are usually identifying a primary headache disorder—meaning the headache itself is the main medical problem ^[4]. However, it is crucial to ensure you do not have secondary hemicrania continua, which is when an underlying, separate medical issue is mimicking the symptoms ^[10].

The diagnostic hallmark of HC is that the pain responds completely to a specific prescription anti-inflammatory medication called indomethacin ^[11].

Safety Warning: A diagnostic indomethacin trial must be closely supervised by a clinician. Do not start, adjust, or use this medication to self-treat, as it carries risks of gastrointestinal bleeding, ulcers, kidney issues, and cardiovascular problems.

Even if your pain completely resolves with a supervised indomethacin trial, your clinician will still consider evaluating you for secondary causes, because these secondary mimics can also respond to the medication ^[10]. Known secondary causes include:

• Structural Causes: Tumors, such as those in the pituitary gland (a small hormone-regulating gland in the brain), or other masses pressing on nerves ^[10][12].
• Vascular Causes: Blood vessel issues like aneurysms (bulging vessels), tears in the neck arteries (cervical artery dissection), or abnormal connections between arteries and veins ^[13][14][15].

Depending on your specific clinical history and examination, your doctor will likely recommend a brain MRI ^[4]. Based on your symptoms, they may also decide to include dedicated pituitary views or vascular imaging—such as an MRA (an MRI-based blood vessel study) or a CTA (a CT-based blood vessel study) ^[10].

When to Seek Urgent Care

Because some secondary causes like blood vessel tears can be dangerous, seek emergency medical care immediately if you experience a sudden “thunderclap” or worst-ever headache, new weakness or numbness, sudden vision loss or major double vision, confusion, fainting, or a fever with a stiff neck.