Although the concept of the mummy flies in the face of biology, mummy rot comes close to being scientifically explicable. By looking at two real-world diseases, we can infer that mummy rot's mechanism of action, on a physiological level, probably involves damage to nerves and blood vessels.

Dr. Eric Lis is a physician, gamer, and author of the Skirmisher Publishing LLC sourcebook, Insults & Injuries.

The average role-playing game has so many elements that make no scientific sense, it can actually be a little shocking to find the ones that do. No matter how creative you are, if you draw from the two most popular system reference documents, there's just no way to conceptualize a dragon or a vampire in a manner that's biologically plausible, at least within our current understanding of biology, but we accept it all in our games on account of the best reason there is: it all makes for good stories. Even within the most entertainingly implausible idea, however, we can often find a little tidbit here and there which, with a bit of imagination, can actually be made to make some sense. Take, for example, the mummy, the classic bandage-wrapped, shuffling undead that is the bane of adventurers in one form or another in pretty much every campaign setting ever devised. Although the concept (and stat block) of the mummy flies in the face of biology, physics, chemistry, and pretty well every science derived from them, one of the mummy's most famous powers -- mummy rot -- actually comes perilously close to being scientifically explicable. Not wholly explicable, but close, if, as the histologists say, you look very closely, then squint and hallucinate. By looking at two real-world diseases, we can infer that mummy rot's mechanism of action, on a physiological level, probably involves damage to nerves and blood vessels.

According to the Pathfinder SRD, mummy rot is a combined curse and disease which drains constitution and charisma over time, and a creature that dies of it turns to dust. That's all well and good in terms of mechanics, but it doesn't actually tell us much about what the disease is or how it works. For a more flavourful description, we must turn to a truly authoritative source. In the excellent Van Richten's Guide to the Ancient Dead, published by TSR in 1994 (and today just a few weeks shy of its twentieth anniversary, as it happens), the noted physician describes mummy rot as follows:

"The victim generally feels no particular discomfort: in fact, the infected area often seems to be immune to minor aches, pains, and injuries... A victim numbed by mummy rot... is prone to ignore minor injuries that he might otherwise attend. This untreated damage frequently leads to serious infection. The lack of feeling in the skin... greatly slows the body’s natural healing powers. A scratch that might disappear in a day or two instead lingers for 10 days or more... The victim breaks out in scabrous sores. In very advanced cases the victim’s ears, nose, and digits shrivel or even fall off. Once the malady reaches this stage, the victim will be scarred for life even if cured."

A doctor will likely find that this description sounds familiar. In fact, it describes something which could be a manifestation of a number of real-world diseases, the most salient of which is leprosy. Leprosy is a bacterial infection which attacks the nerves. As nerves are damaged, people lose sensation in their fingers and toes, and as sensation is lost, the body loses its ability reflexively protect those extremities. In a normal person's life, they're constantly performing movements and actions which can severely damage the hands and feet, but because sensation is intact, we protect ourselves when something is painful or uncomfortable. Even when you're sitting still, you're at risk of damaging your body; sitting in one position for a long period of time cuts of blood circulation to bent limbs of the parts on your body touching a chair, which is why your body is designed to feel uncomfortable and change positions from time to time. Without the ability to sense that a body part is uncomfortable, we bash our fingers, we stub our toes, and we sit long enough that our skin starts to break down and ulcerate. Given time, gangrene sets in and body parts literally rot away on the body. There's your constitution loss. As if that wasn't enough, the disease also damages the skin, causing scaly growths, particularly in cooler areas such as the face and hands. These growths are readily visible and mark the sufferer as having a disease, and there's your charisma loss. Leprosy is spread from coughing and sneezing or from close contact... such as a mummy's touch attack. Of course, mummy rot is a good deal faster and deadlier than regular leprosy, by virtue of being magical and because, for narrative reasons, a disease that will kill a character thirty years later lacks punch.

It's hard to say for certain if the original creators of D&D's mummy rot were directly inspired by leprosy, but it seems clear that Skip Williams was when he wrote Van Richten's Guide to the Ancient Dead.

Just to really put some good ol' Ravenloft-style fear into you, there's another, much more common disease that can cause symptoms like this, and it's one that some of the people reading this already suffer from: diabetes. Diabetes doesn't cause the same sort of visible scarring that leprosy does, but if a diabetic patient's sugars are poorly controlled over many years, one of the various complications that can develop is diabetic neuropathy, nerve damage caused by chronic hyperglycemia. The body's nerves slowly lose efficiency and function, and the longest, thinnest nerves lose function the fastest. Fingers, toes, and the center of the chest lose sensation first, and if it proceeds, the numbness can easily affect large parts of the limbs. Just like in leprosy, numbed fingers and toes become prone to unnoticed and untreated injuries. Diabetic neuropathy is accompanied by damage to the body's smallest blood vessels, so the hands and feet also get poor blood flow and become much slower to heal; tiny wounds don't get better the way they should, leading to gangrene and eventual amputation. Again, this clinical picture is quite similar to that of mummy rot, albeit on a much, much longer time scale.

Naturally, there are aspects of mummy rot that don't make quite as much physiological sense, namely the speed with which it works and, more to the point, the fact that people who die of mummy rot instantly turn to dust. As far as that goes, the best we can do is say that it's magic, shake our heads, and acknowledge that if we insisted on scientific accuracy in all things, we probably wouldn't be playing fantasy games in the first place.