Subarachnoid Hemorrhage (SAH): Symptoms and Risks

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on Genetics & Cardiovascular Health. Browse all Genetics & Cardiovascular Health education

Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space — the thin fluid-filled layer between the brain and the tissues covering it. It is a medical emergency, most often caused by a ruptured brain aneurysm, and recognizing it quickly can be lifesaving. Understanding the symptoms, the risk factors, and the genetic contribution can help you know when to act and when to talk with a provider.

This article covers what SAH is, its warning signs, the modifiable and inherited risks, and the gene variants research has connected to brain aneurysm and vascular integrity. SAH is an emergency: if you suspect it, call emergency services immediately.

What subarachnoid hemorrhage is

SAH occurs when a blood vessel bleeds into the subarachnoid space surrounding the brain. The most common non-traumatic cause is the rupture of an intracranial (brain) aneurysm — a weakened, balloon-like bulge in an artery wall. Trauma can also cause SAH. Because blood in this space raises pressure and irritates brain tissue, the event can escalate rapidly.

Symptoms and warning signs

The hallmark symptom is a sudden, severe headache often described as the worst headache of one’s life or a “thunderclap” headache that peaks within seconds. Other signs include a stiff neck, nausea and vomiting, sensitivity to light, blurred or double vision, brief loss of consciousness, seizures, and sudden confusion or weakness.

Some people experience a smaller “sentinel” headache days or weeks before a major bleed. Any sudden, explosive headache unlike your usual pattern warrants emergency evaluation — do not wait to see if it passes.

Risk factors you can and cannot change

Modifiable risks include high blood pressure, smoking, heavy alcohol use, and stimulant drug use — hypertension and smoking are among the strongest. Non-modifiable risks include increasing age, female sex (risk rises after menopause), and a family history of aneurysm or SAH.

Certain inherited conditions also raise risk, including autosomal dominant polycystic kidney disease and connective-tissue disorders such as vascular Ehlers-Danlos syndrome. Family history is one of the clearest signals that genetics may be involved.

The genetic contribution

Having a first-degree relative who has had an aneurysm or SAH meaningfully increases risk, and genome-wide studies have identified specific loci tied to intracranial aneurysm. SOX17, a gene involved in blood-vessel formation, and a locus on chromosome 9p21 near CDKN2B-AS1 (also called ANRIL) have both been associated with aneurysm risk across large populations.

Genes affecting arterial wall strength also matter. COL3A1 encodes type III collagen, a key structural protein in blood-vessel walls; pathogenic variants cause vascular Ehlers-Danlos syndrome and raise the risk of arterial rupture. These genes describe vascular vulnerability, not certainty of an event.

What genetic insight can and cannot tell you

Genetic analysis can describe tendencies in pathways that influence vascular structure and inflammation. The PlexusDx Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights across biological systems relevant to cardiovascular and connective-tissue health. It provides pathway-level context about your biology — it does not diagnose an aneurysm, screen for SAH, or predict whether a bleed will occur.

Genetics is a guide, not a guarantee. If you have a strong family history of aneurysm or SAH, the right next step is a conversation with a qualified provider about whether imaging or specialist referral makes sense for you — not a home genetic result used in isolation.

Frequently Asked Questions

What does a subarachnoid hemorrhage feel like?

The classic sign is a sudden, extremely severe headache that peaks within seconds — often called a thunderclap or the worst headache of your life. It may come with a stiff neck, vomiting, light sensitivity, vision changes, or loss of consciousness. Treat any such headache as an emergency.

Is subarachnoid hemorrhage hereditary?

Risk can run in families. Having a first-degree relative with a brain aneurysm or SAH raises your risk, and genes such as SOX17, COL3A1, and a 9p21 locus are linked to aneurysm susceptibility. Inherited conditions like polycystic kidney disease also increase risk. Genetics is one factor among several.

Can genetic testing prevent a subarachnoid hemorrhage?

No. Genetic testing describes pathway-level tendencies in vascular and connective-tissue biology. It does not diagnose, screen for, treat, or prevent SAH. People with a strong family history should discuss appropriate imaging and specialist care with a qualified provider rather than rely on a genetic result.

What lowers the risk of subarachnoid hemorrhage?

Controlling blood pressure and not smoking are the two most impactful steps, since hypertension and smoking are leading modifiable risks. Limiting heavy alcohol use and avoiding stimulant drugs also helps. Anyone with a family history should ask a provider whether screening is appropriate for their situation.

Want context on the vascular and connective-tissue pathways in your DNA? Take the Precision Peptide Genetic Test.

This article is part of the PlexusDx Education Hub. Browse all Genetics & Cardiovascular Health education

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use, and it does not diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare provider before beginning any peptide protocol or making changes to your care.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.