Cell death sounds like it should be a single, simple category — a cell stops working, and it dies. Pathologists distinguish sharply between two fundamentally different processes that both end in a dead cell, because the manner of death matters enormously for the surrounding tissue. Apoptosis is death the cell orchestrates itself, cleanly and quietly. Necrosis is death forced on the cell from outside, and it makes a mess that the tissue around it has to deal with.
Apoptosis: a controlled, self-initiated shutdown
Apoptosis, often called programmed cell death, is an active process the cell itself carries out using a specific internal genetic and biochemical machinery, triggered either by internal signals (like irreparable DNA damage) or external ones (like signals from other cells). The dying cell shrinks, its DNA fragments in an orderly way, and its contents get packaged into small membrane-bound fragments that neighbouring cells or immune cells can cleanly engulf and dispose of — critically, without ever releasing the cell's internal contents into the surrounding tissue. This tidy packaging is exactly why apoptosis doesn't trigger an inflammatory response: nothing spills out for the immune system to react to. Apoptosis is happening constantly in a healthy body, eliminating damaged, unnecessary, or potentially dangerous cells (including many that could otherwise become cancerous) without disrupting the tissue around them.
Necrosis: death by injury, and the mess it leaves
Necrosis, by contrast, results from acute injury overwhelming a cell's ability to maintain itself — oxygen deprivation, toxins, physical trauma, or infection can all cause it. Unlike apoptosis's controlled shrinkage, a necrotic cell swells and ruptures, spilling its internal contents, including enzymes and molecules the body treats as danger signals, directly into the surrounding tissue. That spillage triggers an inflammatory response, recruiting immune cells to the area and often causing collateral damage to nearby healthy tissue in the process, which is why necrosis is generally associated with disease and injury rather than normal, healthy tissue turnover the way apoptosis is. A heart attack or stroke, for instance, causes tissue damage substantially through necrotic cell death, with the resulting inflammation contributing meaningfully to the injury beyond the cells that died from oxygen deprivation directly.
What we're still unsure about
The core distinction between apoptosis and necrosis, and the different molecular machinery each involves, is well established pathology, not in dispute. What remains a more active area of research is the fuller picture of cell death, which turns out to be more varied than this classic two-category distinction alone captures — additional forms of programmed cell death with their own distinct mechanisms and inflammatory consequences (such as pyroptosis and necroptosis) have been identified more recently, and researchers are still working out how these additional pathways interact with apoptosis and necrosis, and how manipulating them therapeutically might help treat diseases where cell death goes wrong in either direction — too much, as in degenerative disease, or too little, as in cancer.
This sits inside Cell Injury, Death & Adaptation, one of seven topics in Pathology, one of four domains in Medicine, one of seventeen subjects the app can quiz you on.