How Long Would the Zombie Apocalypse Really Last?

By  · Published on August 8th, 2013


If you’ve spent any time watching movies, reading news stories about bath salts, enjoying AMC original programming, or farting around on Facebook, you’ve encountered the question about whether a zombie apocalypse could actually happen.

Zombie stories range from the absurd (in films like Chopper Chicks in Zombietown) to the allegedly realistic (most recently in World War Z), but they all hinge on the question of what you would do in a worldwide outbreak of brain-eaters.

Now that zombies have become possibly the most revered monster in horror and popular cinema (with Twilight vampires not counting because they aren’t real monsters), some people have wondered how fictional the day rising up is, but since we like to think outside the coffin, we started wondering: If a zombie apocalypse did happen, how long would it actually last?

The Answer: Only a few months

Obviously, the main ingredient needed for a zombie apocalypse is zombies. However, the problem with zombies is they’re dead. Many films and television shows would have you believe that there would be an unending supply of dead bodies on the move during the zombie apocalypse because every dead person would start stumbling around on the search for human flesh. However, one of the things that make zombies so terrifying would be their undoing.

They rot.

Dead bodies follow a predictable pattern of decay, featuring five different stages: fresh, bloat, active decay, advanced decay, and dry/skeletal. During the fresh stage, rigor mortis sets in and body fluids begin to pool. Within hours of death, the body starts to turn on itself, with the bacteria in the digestive tract beginning to literally digest the body from the inside out. Chemical waste creates an acidic environment as putrefaction begins, often within 36 hours. Many zombies seen in movies are in the “fresh” stage, characterized with skin lesions and minor discoloration.

However, within hours or days (depending on the environment), the bloat stage would begin, featuring gaseous buildup and massive discoloration. By this time, the eggs laid by flies in the open orifices would hatch, causing the body to erupt in maggots, which feed on the dead flesh.


By the time the body reaches the active and advanced decay stage, it would be falling apart. The remaining skin would drop away from the bone, and the internal organs and other soft tissues (including the brain itself) would have liquefied, leaving very little zombie.

The final stage of dry/skeletal could remain for years in the open, but there would be no muscles, tendons, or ligaments left to hold the bones together, much less give them mobility.

But exactly how long would that take?

Even though decomposition follows a predictable pattern, many factors contribute to the speed at which it happens. Submerging a body in water slows decomposition by approximately 50 percent, and burying a body can slow decomposition by a factor of eight or more. If a body is embalmed, which removes some of the fluids and preserves the corpse, it can last even longer. Of course, if you follow strict zombie movie rules laid out by George A. Romero in Night of the Living Dead, it is only the recently deceased that get up and walk.

The main environmental factors that affect the decomposition of bodies include temperature and humidity. Warmer, more humid environments promote decay. Cooler and drier climates can delay it a bit. According to Dawnie Wolfe Steadman (Ph.D., D-ABFA), Director of Forensic Anthropology Center at the University of Tennessee:

“In eastern TN where we study decomposition an exposed body can skeletonize within 2–3 weeks in the summer months. The same body may take several months or more in the winter when the temperatures are too low for insects and enteric bacteria (natural bacteria in our intestines) to be active.”

Due to temperature and humidity factors, the undead in the deep south during the summer would rot away quicker than the undead in the cooler months in England, so the folks in The Walking Dead should have a quicker run than those in Shaun of the Dead. Either way, the first wave of zombies would rot away in less time than it would take to make a zombie movie.

This can be observed in nature every day. Dead animal bodies exposed to the environment would decompose in as short as a couple weeks to a few months, depending on the conditions. According to Rachel Renee Bower, graduate student at Penn State University, a 150-pound pig will take only four days in the heat of the summer to reach a state of advanced decay, leaving mostly just the bone and skin. So, the idea of zombies languishing around the countryside for years is not quite accurate… unless the cause of zombies results in making the dead bodies unappealing to bacteria and scavengers… and you live in Alaska. (Note to self: Never move to Alaska!)


So what should you do when the zombies attack?

Ultimately, the advice given by Brad Pitt’s character in World War Z to keep moving and not hide might have been premature. Rather than waging a full-scale war on the undead, it might be better to hunker down and wait it out. Hole up in a shopping mall like in Dawn of the Dead, and you might be able to outlast the hoards of undead as they skeletonize over the course of a few weeks.

Of course, this is assuming there are no outbreaks in a largely populated area.

You’d better aim for the head, just in case.

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