Plaque in arteries is a buildup of fatty material, cholesterol, calcium, cellular waste, and a clotting protein called fibrin that collects inside your artery walls over time. This buildup narrows the space blood flows through and can eventually trigger a heart attack or stroke. The condition is called atherosclerosis, and it’s remarkably common: imaging studies show that about 52% of adults have detectable plaque in their carotid arteries by their early 60s, with prevalence climbing steadily with age.
What Plaque Is Made Of
Arterial plaque isn’t a single substance. It’s a mix of biological materials that accumulate in layers within the artery wall. The main ingredients are fatty deposits (lipids), cholesterol, calcium, dead cells and cellular debris, and fibrin, a stringy protein your body normally uses to form blood clots. Over years or decades, these materials harden and thicken inside the artery lining, creating a deposit that bulges inward and restricts blood flow.
The composition of a given plaque deposit matters more than its size. Some plaques become heavily calcified and stiff. Others remain soft and fatty with a thin outer shell. That distinction, covered below, is what determines whether plaque is dangerous right now or simply worth monitoring.
How Plaque Forms Step by Step
Plaque doesn’t appear overnight. The process starts when cholesterol-carrying particles in your blood slip through the inner lining of an artery and lodge in the artery wall beneath it. This happens most readily at spots where blood flow is turbulent, like branch points where arteries split in two. Once trapped, these cholesterol particles undergo chemical changes: they become oxidized and broken down, which makes them irritating to the surrounding tissue.
Your immune system responds by sending white blood cells called macrophages to clean up the problem. These cells swallow the modified cholesterol, but instead of removing it, they become engorged and turn into what researchers call “foam cells.” Foam cells are essentially immune cells stuffed with fat. They accumulate in the artery wall and form the earliest visible sign of plaque, known as a fatty streak.
Over time, more cholesterol particles arrive, more immune cells pile in, and some of those cells die, leaving behind a growing core of fatty debris. The artery responds by building a cap of fibrous tissue over the deposit, walling it off from the bloodstream. Calcium gradually deposits within the plaque, and the whole structure becomes more complex. This process can begin as early as your teens or twenties but typically doesn’t cause symptoms until decades later, when the plaque has grown large enough to significantly narrow an artery or becomes unstable enough to rupture.
Stable vs. Unstable Plaque
Not all plaque is equally dangerous. The critical distinction is between stable plaque and unstable (or vulnerable) plaque, and the difference comes down to structure.
Stable plaques have a thick, tough fibrous cap covering a relatively small fatty core. They often contain large calcium deposits. These plaques can narrow arteries and reduce blood flow, potentially causing symptoms like chest pain during exercise, but they’re less likely to cause a sudden heart attack. They tend to grow slowly and predictably.
Unstable plaques are the ones that kill. They have a large core of dead cells and fatty debris covered by a thin fibrous cap, sometimes as thin as 23 micrometers, roughly a quarter the width of a human hair. Research published in the American Heart Association’s journals defines a vulnerable plaque as one with a cap thinner than 65 micrometers. These thin-capped plaques are heavily infiltrated by immune cells that weaken the cap further, making it prone to cracking open.
When an unstable plaque ruptures, its fatty interior is suddenly exposed to the bloodstream. Your body treats this like an injury and rapidly forms a blood clot at the site. That clot can partially or completely block the artery within minutes, cutting off blood supply to the heart (heart attack) or brain (stroke). The dangerous paradox of atherosclerosis is that the plaques most likely to rupture are often not the ones causing the most narrowing. A moderately sized unstable plaque can be far more lethal than a large stable one.
What Triggers a Rupture
Plaque rupture can happen spontaneously, but temporary spikes in physical or emotional stress sometimes provide the final push. Triggers documented in research include intense physical exertion, sexual activity, anger, severe anxiety, and cocaine use. Even environmental factors like earthquakes, extreme temperature changes, and acute infections have been linked to increased rupture events.
The mechanism involves your sympathetic nervous system, the same system behind your fight-or-flight response. A sudden surge in heart rate and blood pressure can put mechanical stress on a weakened cap, cracking it open. Stress also increases your blood’s tendency to clot and makes platelets stickier, which amplifies the clotting response once a rupture occurs. This helps explain why heart attacks are most common in the morning hours, when your body’s natural rhythms produce a rise in blood pressure, heart rate, and clotting activity.
How Common Plaque Is by Age
Arterial plaque is far more prevalent than most people realize. A large study published in JAMA Cardiology examining over 5,600 adults found that plaque prevalence in the carotid arteries (the major arteries supplying the brain) rises sharply with each decade of life. Among adults aged 45 to 49, roughly 15% to 38% already had detectable plaque depending on sex and ethnicity. By ages 70 to 74, that number climbed to 57% to 81%. Among non-Hispanic white men aged 80 to 84, 95% had visible carotid plaque.
Men tend to develop plaque earlier than women across all groups studied. The gap narrows with age, particularly after menopause, when women lose the cardiovascular protection that estrogen provides. Having detectable plaque doesn’t necessarily mean you’re in immediate danger, but it does indicate the disease process is underway and that managing risk factors becomes increasingly important.
How Plaque Is Measured
A coronary calcium scan is one of the most common ways to assess plaque buildup. This quick CT scan measures the amount of calcium in your coronary arteries and produces a number called a calcium score.
- Score of 0: No calcium detected. This suggests a low chance of heart attack in the near future.
- Score of 1 to 99: Mild plaque deposits are present.
- Score of 100 to 300: Moderate plaque. This range carries a relatively high risk of heart attack or other cardiovascular events over the next three to five years.
- Score above 300: Extensive plaque disease with the highest heart attack risk.
A calcium score only detects calcified plaque, which tends to be the stable variety. It can miss soft, non-calcified plaques, which are often the more dangerous ones. For this reason, a score of zero doesn’t guarantee zero risk, though it is reassuring. Your doctor may use additional imaging or blood tests alongside a calcium score to get a fuller picture.
Can Plaque Be Reversed?
Plaque can be partially reversed with aggressive cholesterol-lowering treatment, though it doesn’t disappear entirely. Clinical trials using imaging to measure plaque volume inside coronary arteries have shown measurable regression. In one major trial (SATURN), high-dose cholesterol-lowering medication reduced total plaque volume by about 3% to 5% over two years. Another trial conducted in Japan showed reductions of 16% to 18% at 12 months. By contrast, patients on less intensive treatment saw plaque continue to grow.
These percentage changes might sound small, but they represent a meaningful shift. Beyond shrinking plaque volume, treatment also stabilizes existing plaques by thickening the fibrous cap, reducing inflammation, and making rupture less likely. That stabilization effect is probably more important than the size reduction itself, because it’s rupture, not gradual narrowing, that causes most heart attacks.
Lifestyle changes work alongside medication. Regular aerobic exercise, a diet low in saturated fat and processed foods, not smoking, and maintaining a healthy weight all slow plaque progression and reduce the inflammation that drives the disease. These measures are most effective when started early, before significant plaque has accumulated, but they provide benefit at any stage. The artery wall is a living tissue that responds to changes in its environment, and lowering cholesterol levels removes the driving force behind continued plaque growth.