An occlusion is a blockage or closure that prevents normal flow through a passage in the body. The term appears across nearly every branch of medicine, from cardiology to dentistry to eye care, but the core meaning is always the same: something that should be open is partially or fully closed. Understanding what type of occlusion is involved, and where it occurs, determines how serious it is and how it gets treated.
Vascular Occlusion: Blocked Blood Vessels
The most common medical use of “occlusion” refers to a blockage in a blood vessel. A blood clot, fatty deposit, or piece of debris lodges in an artery or vein and restricts or stops blood flow. When this happens, the tissue downstream is starved of oxygen, a condition called ischemia. If the blockage isn’t resolved, that tissue can die.
Blood clots form differently depending on where they occur. In arteries, where blood moves fast under high pressure, clots are built primarily from platelets and tend to appear whitish. In veins, where blood flows more slowly, clots are made mostly of red blood cells and a protein mesh called fibrin, giving them a darker red appearance. These structural differences matter because they influence how well the body (or medical treatment) can break the clot down. Red blood cells packed inside venous clots actually suppress the body’s natural clot-dissolving process, making these blockages harder to clear on their own.
Clots can also break loose and travel. A piece of a venous clot that detaches and reaches the lungs becomes a pulmonary embolism. A clot fragment from the heart or a neck artery that reaches the brain causes a stroke. Globally, peripheral artery disease alone affects an estimated 113 million people over age 40, with prevalence climbing steeply with age to nearly 15% in people aged 80 to 84.
Arterial vs. Venous Symptoms
Arterial and venous occlusions produce noticeably different symptoms. Arterial blockages in the legs cause numbness, weakness, skin color changes, cool skin temperature, hair loss, and wounds that refuse to heal. In severe cases, tissue dies entirely. Pain often follows a predictable pattern, worsening with activity and easing with rest, though it can also strike at night.
Venous blockages look and feel different. They tend to cause swelling, a heavy or achy sensation, visible varicose or spider veins, and throbbing or cramping. The pain typically worsens when you stay in one position for a long time rather than when you’re moving.
Occlusion in the Heart
When a coronary artery becomes completely blocked, the result is a heart attack. Current guidelines from the American College of Cardiology and American Heart Association (updated in 2025) set tight time windows for treatment. The goal is to reopen the blocked artery within 90 minutes of first medical contact, or within 120 minutes if the patient needs to be transferred to a hospital equipped for the procedure. Beyond 12 hours from when symptoms start, the benefit of reopening the artery begins to fade, though some benefit may persist up to 24 hours. After 48 hours with no ongoing symptoms, routine reopening of the blocked vessel has not been shown to help.
An ECG should be obtained and interpreted within 10 minutes of arrival at the emergency department. Blood tests measuring heart-damage proteins are drawn at presentation and again one to two hours later using modern high-sensitivity tests, or three to six hours later with older tests.
Occlusion in the Eye
A retinal artery occlusion happens when the blood vessel feeding the retina becomes blocked, almost always by an embolus, a small clot or piece of plaque that traveled from the heart or a neck artery. More than 90% of cases fall into the nonarteritic category, meaning they’re caused by emboli rather than by inflammatory blood vessel disease.
The hallmark symptom is sudden, painless vision loss in one eye, occurring over seconds. Vision can range from barely perceiving light to being able to count fingers. Some people experience brief episodes of temporary vision loss (called amaurosis fugax) in the days or weeks before the full occlusion hits. On examination, the retina appears pale with a characteristic cherry-red spot at the center. Because this type of occlusion signals underlying cardiovascular disease, it’s treated as a medical emergency requiring both eye-specific and systemic evaluation.
Dental Occlusion: How Your Teeth Meet
In dentistry, occlusion simply means the way your upper and lower teeth come together when you close your mouth. A normal, or “ideal,” occlusion means the teeth align properly with each other. When they don’t, it’s called malocclusion.
Dentists classify malocclusion into three main classes based on how the upper and lower first molars line up. In Class I, the molars align correctly but there may still be crowding, protruding front teeth, or a crossbite. In Class II, the upper jaw sits too far forward relative to the lower jaw, creating what’s often called an overbite. This class has two subtypes: one where the upper front teeth flare outward with excessive horizontal overlap, and another where the upper central teeth tilt inward and may be overlapped by the teeth next to them. In Class III, the lower jaw sits ahead of the upper jaw, so the bottom teeth protrude in front of the top teeth, sometimes called an underbite.
Malocclusion isn’t just a cosmetic issue. Poor dental occlusion can contribute to uneven tooth wear, jaw pain, difficulty chewing, and temporomandibular joint problems over time.
Intestinal Occlusion: Bowel Obstruction
An occlusion in the bowel means something is preventing food and digestive contents from passing through the intestines. These blockages fall into two categories. Mechanical obstruction involves a physical barrier: scar tissue (adhesions) from previous surgery, a tumor growing into the intestinal wall, or even a gallstone that’s migrated into the bowel. Functional obstruction, often called ileus, occurs when the bowel simply stops contracting. There’s no physical blockage, but the muscles of the intestinal wall aren’t pushing contents forward, often due to inflammation, metabolic imbalances, or the effects of surgery.
Both types produce similar downstream problems. Contents stall, fluid accumulates, the bowel swells, and bacteria begin to overgrow. In mechanical obstruction, there’s a clear transition point where the bowel is distended above the blockage and collapsed below it. In functional obstruction, the entire bowel tends to be sluggish and uniformly distended.
How Occlusions Are Diagnosed
The tools used to find an occlusion depend on where it’s suspected. For blood vessel blockages, CT angiography is the workhorse in emergency settings. It reliably detects narrowing or complete blockage in large arteries, including the carotid arteries in the neck and the major arteries in the brain. Many stroke centers use a combination of non-contrast CT, CT angiography, and CT perfusion imaging as their standard evaluation.
Duplex ultrasound, which combines traditional ultrasound with blood flow measurement, is the go-to screening tool for narrowing in the carotid arteries. It’s noninvasive, widely available, and doesn’t require radiation or contrast dye. Catheter-based angiography, where a thin tube is threaded into the blood vessels and dye is injected directly, remains the gold standard for the most detailed view of blood vessel anatomy. However, because it’s invasive, it’s now used more often for treatment than for diagnosis alone.
How Occlusions Are Treated
Treatment depends entirely on the type, location, and severity of the occlusion. For blood vessel blockages, the main approaches are clot-dissolving medications (thrombolysis), balloon angioplasty to physically widen the vessel, and stent placement to hold it open. These techniques are often combined. In cases of severe artery disease in the brain’s blood supply, for example, placing a stent first can restore enough blood flow to buy time while clot-dissolving drugs work on the remaining blockage. Stenting also reduces complications like artery spasm and tearing of the vessel wall that can occur with balloon angioplasty alone.
For coronary artery occlusions causing a heart attack, the primary treatment is catheter-based intervention to physically reopen the blocked artery. If that can’t happen within two hours and symptoms started less than 12 hours ago, clot-dissolving medication given intravenously is the alternative. If that medication fails to restore flow, the patient proceeds to an emergency catheter procedure.
Dental malocclusion is managed with orthodontic treatment, ranging from braces to surgery depending on the severity and underlying skeletal relationship. Bowel obstructions may resolve with rest, decompression through a tube, and time (especially functional obstruction), or they may require surgery to remove the physical blockage.