Plaque builds up in arteries through a slow, multi-stage process that begins with cholesterol particles slipping beneath the inner lining of artery walls. What starts as microscopic fatty deposits in childhood can, over decades, grow into hardened blockages that restrict blood flow or rupture suddenly. The process involves your immune system, chronic inflammation, and structural remodeling of the artery wall itself.
It Starts Earlier Than Most People Think
Atherosclerosis begins in childhood. Cholesterol and its byproducts deposit as fatty streaks in the inner walls of large arteries during the first decade of life. These streaks aren’t dangerous on their own, but they’re the foundation for everything that follows. During adolescence, some of these fatty streaks accumulate more lipid and begin developing a fibrous cap, forming what’s called a fibrous plaque. By the time most people start thinking about heart disease in their 40s or 50s, the process has been underway for decades.
This long timeline is why risk factors in early life matter. Childhood obesity, high cholesterol in young adults, and smoking in your 20s aren’t just future concerns. They’re actively shaping the artery walls you’ll rely on later.
How Cholesterol Gets Trapped in the Artery Wall
The process begins when cholesterol-carrying particles in the blood penetrate the endothelium, the thin inner lining of an artery. Normally, this lining acts as a barrier, but high blood pressure, high blood sugar, cigarette smoke, and other irritants damage it over time. Once the lining is compromised, cholesterol particles slip through and lodge in the layer just beneath it.
Once trapped, these particles undergo chemical changes. They become oxidized, essentially turning rancid. The body treats oxidized cholesterol the way it treats any foreign invader: it sends immune cells to deal with the problem. Inflammatory signals recruit white blood cells called monocytes from the bloodstream into the artery wall. Once inside, these monocytes transform into macrophages, larger immune cells designed to engulf and digest debris.
Here’s where things go wrong. The macrophages swallow the oxidized cholesterol, but they can’t break it down efficiently. Instead, they become engorged with fat, transforming into what pathologists call foam cells. These bloated, cholesterol-stuffed immune cells are the building blocks of plaque. As more foam cells accumulate and die, they leave behind a growing pool of lipid debris inside the artery wall.
Inflammation Drives the Process Forward
Plaque buildup isn’t just a passive accumulation of fat. It’s an active inflammatory process at every stage. The foam cells and damaged tissue release chemical signals that recruit even more immune cells, creating a self-reinforcing cycle. More macrophages arrive, consume more cholesterol, become more foam cells, and release more inflammatory signals.
One marker of this inflammation is C-reactive protein (CRP), a substance the liver produces in response to inflammation throughout the body. CRP doesn’t just passively reflect what’s happening in the arteries. It actively makes things worse by reducing the artery’s ability to relax, increasing the stickiness of the vessel lining so more immune cells can attach, and promoting the recruitment of additional monocytes into the growing plaque. It also contributes to plaque instability, making a rupture more likely down the line.
This is why conditions that cause chronic, low-grade inflammation, such as diabetes, obesity, autoimmune diseases, and even gum disease, are linked to faster plaque progression. The inflammation doesn’t have to originate in the arteries themselves to accelerate the process.
What Plaque Is Actually Made Of
A mature plaque isn’t a simple blob of cholesterol. It’s a complex structure with distinct layers. At its core is a pool of lipid debris, dead foam cells, and cellular waste called the necrotic core. Surrounding this core is fibrous tissue made of collagen, along with smooth muscle cells that migrate in from the artery wall. Over time, calcium deposits form within the plaque, similar to the way calcium hardens bone.
Early plaques tend to be soft, composed mostly of extracellular lipid and fibrous tissue without significant calcium. As plaques mature over years and decades, they calcify. The pattern and extent of that calcification play a major role in whether a plaque remains stable or becomes dangerous.
Stable Plaques vs. Dangerous Ones
Not all plaques are equally threatening. A stable plaque typically has large, dense calcium deposits and a thick layer of fibrous tissue covering it. It may narrow the artery significantly, even causing symptoms like chest pain during exertion, but it’s less likely to cause a sudden heart attack. Think of it as a solid, walled-off bump inside the artery.
Unstable plaques are a different story. These have a large necrotic core filled with lipid debris, covered by a thin fibrous cap. Research has established that when this cap thins to 65 micrometers or less (thinner than a human hair), the plaque becomes vulnerable to rupture. In arteries where plaques have actually ruptured, the average cap thickness was just 23 micrometers. These thin-capped plaques also show heavy infiltration by macrophages and immune cells, which actively digest the collagen holding the cap together.
The calcium pattern matters too. Stable plaques tend to have diffuse, sheet-like calcification (found in about 51% of stable plaques). Unstable plaques, by contrast, show speckled, fragmented microcalcification, a pattern found in 67% of the most dangerous lesions. Small calcium fragments may actually weaken the structure, while large, solid calcium deposits reinforce it.
When a vulnerable plaque ruptures, the necrotic core is exposed to the bloodstream. The body responds the same way it does to any wound: it forms a blood clot. That clot can partially or completely block the artery in minutes, cutting off blood flow. If it happens in a coronary artery, the result is a heart attack. In an artery feeding the brain, it’s a stroke.
Measuring How Much Plaque You Have
A coronary calcium scan uses a CT scanner to detect and measure calcified plaque in the heart’s arteries. The result is an Agatston score. A score of zero means no detectable calcium and suggests a low near-term risk of heart attack. A score of 100 to 300 indicates moderate plaque deposits and a relatively high risk of a heart attack or other cardiac event within three to five years. A score above 300 signals more extensive disease and higher risk. Results can also be expressed as a percentile compared to others of the same age and sex, with scores at or above the 75th percentile linked to significantly higher heart attack risk.
It’s worth noting that a calcium scan only detects calcified plaque. Younger people with early-stage disease may have soft, noncalcified plaques that won’t show up on this test. A zero score doesn’t guarantee clean arteries, but it does indicate that plaque hasn’t progressed to its more advanced, calcified stages.
Slowing, Stopping, and Even Reversing Plaque
The most effective way to slow plaque buildup is lowering the amount of cholesterol available to infiltrate artery walls. The 2026 guidelines from the American College of Cardiology and the American Heart Association set specific targets based on risk level. For people who already have cardiovascular disease and are at very high risk, the recommended LDL cholesterol goal is below 55 mg/dL. For those at high risk but without established disease, the target is below 70 mg/dL. For people at borderline or intermediate risk, below 100 mg/dL is the goal.
These targets are lower than many people realize, and they reflect strong evidence that aggressive cholesterol lowering can actually shrink plaque. In one study using MRI to track plaque volume over six months of cholesterol-lowering therapy, plaque volume decreased by 12%. That’s not just slowing progression. It’s partial reversal. The combination of lowering LDL cholesterol and reducing inflammation appears to stabilize plaques by thickening the protective fibrous cap and shrinking the dangerous necrotic core.
Beyond cholesterol management, the controllable factors that drive plaque buildup are the ones you’d expect: high blood pressure damages the artery lining, high blood sugar accelerates inflammation, smoking introduces toxins that injure the endothelium, and physical inactivity allows metabolic risk factors to compound. Each of these acts on a specific part of the plaque-building process, which is why addressing all of them together produces better results than focusing on any single factor.