"What happens after we die?" That's probably the oldest question in history. And the answer is simple: we become worm food. Which is to say, we decompose. And a whole lot happens to us before (and as) we become worm food, too. The decomposition of corpses is more complicated than you probably imagine. How do bodies decompose, step by step? This list includes many body decomposition facts, so you can know what it's like to decompose before you do so yourself.
First, the basics: decomposition of human (and animal) corpses occurs in five general stages: fresh, bloat, active decay, advanced decay, and dry/remains. At every stage, there are specific chemical processes as well as specific types of animals and fungi that produce distinct effects on the corpse. Along with these general stages, there are two chemical stages of decomposition, called autolysis and putrefaction. Autolysis, sometimes called "self-digestion," is the destruction of a cell through the action of its own enzymes. Putrefaction is the decomposition of proteins and the eventual liquefaction of connective tissues and internal organs.
The timing of these processes is one of the main things used by forensic experts in determining time of death when bodies are discovered at under mysterious circumstances. However, many factors influence the speed at which these stages occur, including temperature, moisture, and whether the body was buried. And of course, chemical preservation techniques such as embalming can interfere with, and even postpone, these processes for surprisingly long periods of time.
That said, let's get to the good stuff. Read on for some stand-out body decomposition facts, to impress all your friends at parties. If your friends are weird enough, that is.
Immediately after you die, you enter the first stage of death: pallor mortis. You may look generally as you did in life, but your skin (especially for light-skinned individuals) will be ghostly white and pale. This is caused when the capillaries cease functioning and blood leaves the surface of the skin. Your body will also go limp.
After death, your body will begin to cool down to the temperature of the surrounding environment. Generally your body will drop about 1.5 degrees until it matches room temperature, though it will likely feel much colder to the touch, a trick of perception caused by expecting a human to feel warm. (In addition, some bodies are kept cool before a wake or viewing, which might also explain why they feel surprisingly cold to the touch.)
More uncommonly, your skin may actually warm to reach the ambient temperature of the environment - for example, if you die in a very hot desert and your living body had been working to keep you cool.
Between 20-30 minutes after you die, all the blood in your veins and arteries pools into the interstitial tissues of your body. Basically, this means that your heavy red blood cells, no longer being pumped by your heart, settle out from your blood serum and pool at the lowest part of your corpse (with "lowest" dependent on how you were positioned when you died). Livor mortis produces purplish-red patches of skin that can look like giant bruises, but does not occur on parts of the body that are touching the ground, because capillaries there are compressed.
This is the stage that coroners and other forensic investigators are talking about when they mention "lividity." They can use the presence or absence of livor mortis to approximate the time of death. More importantly, though, they can use it to tell whether your body has been moved post-mortem. For instance, if you were found lying prone, but all the livor mortis was on your back, forensic examiners could instantly determine that someone had moved your body after you died.
Along with chemical and physical changes, there is a whole sequence of ecological succession associated with your corpse. Your body becomes an engine of life for decomposer species, each of whom arrive at your remains at specific stages of decomposition.
Just after you die, all those flies that are always trying to get into your wounds or mouth or ears finally get their chance. Blow flies, flesh flies, and house flies invade any available bodily openings and begin laying eggs or depositing maggots on your flesh. The eggs hatch and maggots move deeper into your body, usually within the first 24 hours. The life cycle of these little baby pests is so precisely known that, along with lividity, it can be used by forensic experts to indicate the time of your death.