How blood vessel walls weaken over time
An aneurysm forms when the wall of an artery becomes thin and weak, then bulges outward like a balloon. This bulge happens because the inner layers of the artery lose their strength. The wall is made of three layers — a tough outer layer, a muscular middle layer, and a smooth inner lining — and when the middle muscular layer deteriorates, the artery can no longer hold its shape against the pressure of blood flowing through it.
The weakening usually happens gradually over years or decades. Blood constantly pushes against artery walls with each heartbeat, and if those walls are damaged or structurally weak, they eventually give way. The location matters: aneurysms most commonly form in the aorta (the largest artery leaving the heart), in arteries at the base of the brain, or in arteries behind the knees and in the abdomen.
Key Takeaways
- High blood pressure is the single most common cause of aneurysms, because constant force against weakened artery walls causes them to bulge.
- Smoking damages the inner lining of arteries and makes the muscular layer more likely to weaken, significantly raising aneurysm risk.
- Some people inherit a genetic tendency toward weak connective tissue, which makes aneurysms more likely even at younger ages.
- Atherosclerosis — the buildup of plaque inside arteries — damages the artery wall and creates conditions where aneurysms can form.
- Infections, trauma, and certain inflammatory conditions can also weaken artery walls, though these cause fewer aneurysms than high blood pressure or smoking.
High blood pressure as the leading cause
High blood pressure damages artery walls over time and is the most common cause of aneurysms. When pressure inside arteries stays elevated — whether from genetics, diet, stress, or kidney disease — the constant force wears down the muscular middle layer. The inner lining develops tiny tears, and the wall becomes less elastic. Eventually, a section of the artery can no longer withstand the pressure and begins to bulge.
This is why people with untreated high blood pressure face a much higher risk. The longer blood pressure remains high, the more damage accumulates. Even people whose pressure is only moderately elevated over many years can develop aneurysms. This is one reason doctors screen for high blood pressure starting in childhood — catching it early and treating it prevents years of artery damage.
Smoking and its direct damage to artery walls
Smoking is the second leading cause of aneurysms and damages arteries in multiple ways. Tobacco smoke contains chemicals that directly injure the inner lining of blood vessels. This injury triggers inflammation, which weakens the muscular layer underneath. Smoking also reduces the amount of oxygen in the blood, which starves artery walls of the nutrients they need to stay strong.
People who smoke are roughly five times more likely to develop an abdominal aortic aneurysm than people who have never smoked. The risk remains elevated for years even after quitting, though it does gradually decrease. Smoking combined with high blood pressure creates an especially dangerous situation, because both conditions are working to weaken the same artery walls.
Genetic factors and inherited connective tissue disorders
Some people inherit genes that make their connective tissue weaker than average. Conditions like Marfan syndrome, Ehlers-Danlos syndrome, and Loeys-Dietz syndrome all affect the proteins that give artery walls their strength. People with these conditions can develop aneurysms at younger ages and sometimes without the usual risk factors like high blood pressure or smoking.
Even without a diagnosed genetic disorder, aneurysms sometimes run in families. If a close relative — a parent or sibling — has had an aneurysm, your own risk is higher. Doctors now recommend screening for abdominal aortic aneurysm in men over 65 who have a family history, even if they have no other risk factors. Genetic testing is available for people with a strong family history or symptoms that suggest an inherited condition.
Atherosclerosis and plaque buildup inside arteries
Atherosclerosis — the buildup of plaque made of cholesterol, fat, and other substances inside artery walls — weakens the artery structure and creates conditions where aneurysms form. The plaque damages the inner lining and triggers chronic inflammation. Over time, this inflammation eats away at the muscular layer, leaving the artery wall thin and prone to bulging.
Atherosclerosis develops when cholesterol levels are high, blood pressure is elevated, or when you smoke. It often coexists with high blood pressure, so people with both conditions face compounded risk. Controlling cholesterol through diet, medication, or both can slow atherosclerosis and reduce aneurysm risk.
Infections and inflammatory conditions that weaken arteries
Certain infections can directly attack artery walls and cause them to weaken. Syphilis, tuberculosis, and some fungal infections have historically caused aneurysms, though these are now less common in developed countries because of antibiotics and vaccines. More recently, infections from contaminated medical devices or procedures can damage arteries at the site of injury.
Inflammatory conditions like vasculitis (inflammation of blood vessels), lupus, and giant cell arteritis can also weaken artery walls. These conditions cause the immune system to attack blood vessel tissue, creating inflammation that damages the muscular layer. People with these diagnoses should work with their doctors to control inflammation and monitor for aneurysm development.
Trauma and injury to blood vessels
A direct injury to an artery — from a car accident, gunshot wound, or surgical procedure — can damage the vessel wall and lead to an aneurysm. The injury may not cause immediate symptoms, but scar tissue forms as the artery heals, and this scar tissue is weaker than the original wall. An aneurysm can develop weeks, months, or even years after the original injury.
Medical procedures that involve inserting catheters or other instruments into arteries carry a small risk of causing this type of damage. Doctors take precautions to minimize injury, but it remains a known complication. People who have had arterial procedures should follow up with their doctors as recommended and report any new symptoms.
Age and the cumulative effect of artery damage
Aneurysms become more common with age because artery damage accumulates over decades. A 70-year-old has had 70 years of blood pressure, smoking exposure, or other risk factors working on their arteries. The muscular layer naturally becomes less elastic with age, even in people without high blood pressure or other conditions.
This is why screening recommendations often focus on older adults. Men over 65 with a history of smoking, high blood pressure, or a family history of aneurysm are offered one-time ultrasound screening for abdominal aortic aneurysm. Women over 65 with the same risk factors may also be screened, though the recommendations vary by organization. Screening catches aneurysms before they rupture, which is the goal of prevention.
Frequently Asked Questions
Can you feel an aneurysm forming?
Most aneurysms cause no symptoms while they are forming and growing. You cannot feel the artery wall weakening or bulging. Many people discover an aneurysm only by accident during imaging done for another reason. This is why screening is important for people at high risk — it finds aneurysms before symptoms appear.
Does high cholesterol alone cause aneurysms?
High cholesterol contributes to atherosclerosis, which can weaken artery walls, but it is not usually the sole cause. High blood pressure and smoking are more direct causes. However, high cholesterol combined with high blood pressure significantly increases risk, so controlling both matters.
If my parent had an aneurysm, will I definitely get one?
No. Having a family history means your risk is higher than average, but it does not mean you will develop an aneurysm. You can reduce your risk by controlling blood pressure, not smoking, managing cholesterol, and maintaining a healthy weight. Talk to your doctor about whether screening is right for you.
Can aneurysms be prevented?
You cannot prevent all aneurysms, especially if you have inherited genetic factors. However, you can significantly reduce your risk by controlling high blood pressure, not smoking, managing cholesterol, and staying physically active. These steps protect artery walls from the most common types of damage.
How fast do aneurysms grow?
Growth rates vary widely. Some aneurysms grow slowly over years and never rupture. Others grow more quickly. Doctors monitor aneurysms with repeat imaging to track growth and decide when treatment is needed. The size and location of the aneurysm, along with your other risk factors, determine how often you need imaging.