Healthy lungs are soft, spongy organs that are pinkish in color, roughly cone-shaped, and together weigh about 1,000 grams (just over 2 pounds) in an adult. They sit on either side of your heart inside the ribcage, protected by thin membranes and filled with millions of tiny air sacs that give them their characteristic spongy texture. What “normal” looks like varies depending on whether you’re looking at the outside surface, a chest X-ray, a CT scan, or a microscope slide, and it also changes naturally with age.
Color, Texture, and Surface
A young, healthy lung that has never been exposed to significant air pollution is light pink with a smooth, glistening surface. That shiny appearance comes from the pleura, a thin membrane that wraps tightly around each lung like a second skin. Between this outer layer and a matching layer lining the inside of the chest wall sits a tiny space containing just a few milliliters of fluid. This fluid acts as a lubricant, letting the lungs slide smoothly against the chest wall with every breath.
In practice, perfectly pink lungs are rare in adults. Almost everyone who lives in a city or industrialized area develops some degree of dark speckling on the lung surface, a harmless carbon pigment deposit called anthracosis. This is considered a normal finding in the general urban population and is distinct from the dense black or slate-grey discoloration seen in coal miners or heavy smokers. So if you see photos of lungs with faint grayish patches, that doesn’t necessarily mean disease.
Size and Shape
Each lung is roughly cone-shaped, with a broad base that rests on the diaphragm and a narrow top (the apex) that extends just above the collarbone. During normal breathing, a healthy adult lung stands about 24 centimeters tall, stretching to around 27 centimeters when you take the deepest breath you can. Together, both lungs hold an average of about 6 liters of air at full capacity, though this varies with height, sex, and age.
The two lungs are not identical. Your right lung is larger and divided into three sections called lobes: an upper, a middle, and a lower. Your left lung has only two lobes because it needs to make room for your heart. A small indentation on the left lung called the cardiac notch is where the heart nestles against it. This size difference is completely normal and is why, if you place your hand over the center of your chest, you can feel your heartbeat slightly to the left.
What You See on a Chest X-Ray
On a standard chest X-ray, healthy lungs appear as two large, dark fields on either side of the bright white silhouette of the heart. They look dark because air doesn’t block X-rays the way bone and soft tissue do. Within these dark fields, you can see a branching network of faint white lines radiating outward from the center of the chest. These are blood vessels carrying blood to and from the lungs.
A few specific features signal that everything is normal. The blood vessels should taper as they move outward and should not be individually visible in the outer third of the lung fields. The bottom corners of the lungs, where they meet the diaphragm, should form sharp, crisp angles (called costophrenic angles). If those angles look blunted or hazy, it can indicate fluid buildup. The right side of the diaphragm normally sits slightly higher than the left because the liver pushes up from below.
What You See on a CT Scan
A CT scan slices through the chest in cross-section and shows far more detail than a standard X-ray. In a healthy person, the lung tissue appears uniformly dark gray, reflecting its air-filled, spongy nature. Blood vessels show up as bright white dots and lines branching through that gray background. There should be no patches of hazy whiteness (called ground glass), no areas of abnormal thickening, and no visible fluid collections. The airways, starting from the windpipe and branching into smaller tubes, should have thin, smooth walls without narrowing or bulging.
Microscopic Structure of Lung Tissue
Zoom in far enough and healthy lung tissue looks like a honeycomb of tiny air sacs called alveoli. Adults have roughly 300 million of them, and their walls are extraordinarily thin, less than 0.1 micrometers in places. This extreme thinness is what allows oxygen and carbon dioxide to pass between the air you breathe and your bloodstream.
Three types of cells make up each alveolus. The first type covers about 70% of the inner surface: flat, paper-thin cells built specifically for gas exchange. The second type is rounder and bulkier, covering only about 7% of the surface. These cells produce surfactant, a slippery substance that keeps the air sacs from collapsing in on themselves like a wet plastic bag. Under a microscope, you can see tiny granules of surfactant packed inside these cells. The third type is a cleanup crew: immune cells that patrol the air sacs, swallowing dust, bacteria, and debris before they can cause harm.
Separating each alveolus from its neighbor is a thin wall threaded with the tiniest blood vessels in the body. Blood flows through these vessels in a layer so thin that oxygen can cross into it almost instantly with each breath.
How Normal Lungs Change With Age
Even in perfectly healthy people, lungs look different at 70 than they do at 30. The alveoli gradually enlarge, and the number of small blood vessels decreases, a combination sometimes called “senile lung.” On a CT scan, this can look similar to early-stage emphysema, but it’s a normal part of aging rather than a disease.
The cartilage rings that hold airways open begin to calcify. By ages 60 to 79, cartilage calcification in the windpipe and large airways shows up in 40 to 65% of people. Airway walls also tend to thicken slightly due to collagen buildup, and mild widening of the airways becomes common even in people with no respiratory symptoms. Fine, web-like lines near the base of the lungs are another frequent finding on CT scans of older adults and, as long as they aren’t accompanied by other structural distortion, are generally considered a normal age-related change rather than a sign of lung disease.
The chest wall itself also shifts. Rib cartilage calcifies, muscle mass decreases, and the overall shape of the ribcage widens from front to back while narrowing side to side. These changes can make chest X-rays look subtly different in older adults, which is why radiologists always factor in a patient’s age when reading imaging studies.