How to Create a Fictional Illness for Your Story

Whether you need a fictional disease to write your next post-apocalyptic heartbreak thriller, or you want to create a story that centers around an alien parasite, carefully crafting that fictional illness is essential. 

Characters can get sick in any genre, but sci-fi, post-apocalyptic, fantasy, and dystopian stories often utilize diseases and other conditions that have no place in reality. Whether you want to put your own spin on a classic fictional ailment like lycanthropy or zombies, or you want to create an entirely new illness from scratch, breaking it up into manageable sections can be a great way to get started.

Designing Symptoms for the Fictional Illness

The most important part of creating a fictional illness, and the part you should think about first, is how the illness manifests itself. What are the symptoms, and how severe are they? Do they change over time as the illness progresses? What parts of the body are affected? Are there different distinct stages to the illness? 

It’s important to keep in mind that symptoms often go hand-in-hand with one another. If a character has a fever, for example, they may also be dizzy, sweaty, and weak. If they have congestion, they’ll probably also be dealing with a headache and a dry mouth from being unable to breathe through their nose. A bad cough can contribute to a sore throat and shortness of breath. Keep this in mind when you are considering which symptoms to include as part of your fictional illness!

When you’re in this period of brainstorming, it can be helpful to make a list of different symptoms you want to include. If you want to break the disease up into stages, a list will make it easier to see how to divide things up and make symptoms more or less severe as time goes on. 

Supernatural or magical influence is also an important thing to keep in mind. If your disease stems from a curse or some other magical influence, you can get as wild and unrealistic as you want with your symptoms. Eyes can change colors, new body parts can sprout, plants can grow from people’s scalps, people can start glowing in the dark, limbs can turn to dust, etc. Consider the popular fictional condition Hanahaki Disease, where a victim of unrequited love coughs or vomits up flower petals. 

The Cause of the Fictional Illness

Now that you have an idea of what your fictional illness looks like, you need to start thinking about how someone actually gets sick with it to begin with. You need to consider not only where the disease comes from, but also how it starts and spreads. 

First, let’s figure out where the illness originates from. Is it a virus that evolved from other animals? Is it a parasite from space? Is it a form of cancer? Does it come from fungus spores? Being bitten by a supernatural creature? Unrequited love? Magic backfiring? A curse? Finding out how a person actually gets sick in the first place is one of the most important aspects to the plot.

Once a person is sick with the disease, however, you need to consider how the disease spreads to other people. Most real illnesses spread through the air, water, or bodily fluids, but you aren’t limited to those options when it comes to fiction. A person’s aura could be infectious, or their mere presence could be enough for others to catch what they have. If the disease started as a result of some sort of delusion or mania (like Hanahaki Disease), simply sharing ideas could be enough for the sickness to spread. 

Of course, there are more gruesome choices as well. Take the zombies in The Last of Us, for example. Those zombies are based on Cordyceps, a type of fungus that takes root inside of a bug and takes over its body. The fungus grows inside the insect until the poor bug dies, and then the fungus releases its spores into the air to then take over other unsuspecting bugs. Naturally, you could apply a similar concept to a condition for humanoids, in which the disease spreads via spores that come from somewhere on the person’s body. Of course, imagining a type of grotesque mushroom-thing that grows on or inside a human being and takes control of them is terrifying—but that’s why it makes for such a good zombie game. 

You can check out Zombie Writing Prompts and Story Ideas if you want to flex your own zombie writing skills. 

Keep in mind that conditions can also be inherited. A character can end up with a condition simply because one of their parents had it. Admittedly, this isn’t the most exciting choice, but it is still an option to consider. Conditions can also spread more than one way, after all. 

Variations and Mutations for Your Fictional Disease

Many diseases and other conditions have variants, and likewise, you should consider if you want your fictional illness to have different strains. These variants can vary in severity, longevity, survivability, and even which parts of the body are affected. 

When you’re making variants for your fictional illness, decide which elements you want to keep the same, and which elements you want to change. If you’re changing up the symptoms, are you changing which symptoms appear entirely, or are you altering the severity at which they occur? Do you want to make a particularly deadly variant for an otherwise mostly benign disease? Do you want the disease to affect different people (such as those in different age groups) differently? Does the disease manifest differently in areas of different climates? If your story contains different humanoid species, does the illness affect all of those different humanoids equally? 

Over the course of your story’s history, new variants of the disease can pop up if it is prone to mutation. Some diseases mutate quickly, like influenza—that’s why a different flu shot is available each year. Other diseases, such as smallpox, can be completely eradicated because of their inability to evolve quickly. However, even diseases that aren’t prone to mutations can evolve if the right conditions are met, such as slow vaccination rollout, a large percentage of the population infected, it moving through a population slowly, impacting the infected person’s immune system, and being treated poorly or improperly. 

A successful mutation is one that allows the pathogen that causes the disease to survive better. This could mean it becomes resistant to treatments or environmental factors, can spread to other species, or survive longer outside of a host body. Of course, when dealing with magical or supernatural illnesses, nothing is really off the table. If you want your story to contain multiple different kinds of vampires, for example, you can do that, and no one is likely to question how that works.

As a side note, if you’re looking to write your own story about Vampires, might I suggest: Writing Prompts About Vampires.

Curing the Fictional Disease

At this point, you should have your fictional illness figured out pretty well. Now, you have to start thinking about a cure.

First things first: can it even be cured?

If the illness can be cured, then what is the process for it? Does it go away on its own without medical intervention? Does it require surgery or medication? Is it only treatable with some sort of ritual or magic spell? Is it a curse that must be broken by some other means? Is there some other form of treatment that relies on future tech or other fictional technology? Does the treatment differ depending on which strain a character has?

You should also consider what recovery is like for an afflicted person seeking treatment. Treatments for different illnesses vary in how difficult and expensive they are. Radiation therapy and chemotherapy are notoriously disruptive to daily life and extremely taxing to experience, whereas taking an over-the-counter pill is quick, easy, and relatively non-disruptive (as long as there are no serious side effects to the medication). What do you want a character’s treatment journey to look like? 

If the illness cannot be cured, what efforts are doctors and scientists making to develop a solution? If it cannot be cured, can it be prevented? Is there a vaccine? How difficult is it for governments to orchestrate large-scale vaccination efforts? 

If there is no cure available, how do people sick with the fictional disease manage their symptoms? Are there options available for them to manage their pain and prevent the disease from worsening? Will the disease continue to progress until it ultimately results in the character’s death? 

How Survivable is the Illness?

Next, you need to consider what an infected person’s odds of survival are after they contract this disease. You should also consider what factors make a person more likely to succumb to the condition, such as age, general health, diet, level of activity, and whether or not they smoke or engage with other controlled (or illegal) substances. Additionally, keep in mind the area of the body that is affected by the disease. A person who smokes or already has trouble with their lungs is going to have a much harder time recovering from a respiratory illness than someone whose lungs work fine. 

It’s also important to keep in mind that even a relatively low mortality rate can have devastating effects on a population. If only 15% of people who contract the disease end up dying to it, it could still potentially kill almost 50 million people if it managed to infect everyone in the United States. 

Even if you know you want your fictional disease to have a 100% mortality rate, you should still consider how fast it would progress in different populations based on the above factors. A person having 1 week left to live is a lot different from having 5 weeks to live, after all. 

After Recovering from the Fictional Illness

Just because a person has recovered from an illness does not mean they will ever be the same again. They could make a full recovery, sure, but severe illnesses often have a way of leaving long-term consequences in their wake. For example, I got sick in college with some unidentified virus, and ever since then I’ve been lactose intolerant. It’s been about 5 years since then (as of writing this) and I still can’t eat dairy. 

Whenever a person’s body is under extreme physical stress for an extended period of time, or an area of their body becomes weakened or damaged due to illness, it stands to reason that it isn’t going to function perfectly for awhile afterward (or ever again). Some examples of this are gastrointestinal problems (like lactose intolerance), new allergies developing, hormonal or menstrual changes, a weakened respiratory system or lasting cough, and blood pressure or blood sugar changes. However, there are also some more unlikely consequences, like the phenomenon of “COVID toes.”

In some cases, an illness can even leave a person permanently disabled. This is obvious in cases where part of the treatment involves removing a body part, but there are many other situations in which a person can be considered disabled after their illness. They might have persistent pain that never goes away, their brain could be damaged, they could go blind or deaf, or they could lose fine motor control. 

You obviously don’t have to give a character lasting symptoms long after the illness is gone, but it is an important thing to keep in mind. If you do want to include that as part of your fictional illness, then you should start by looking at the symptoms first. Which of the symptoms are the most damaging? Which ones are most likely to have a lasting impact, and to what parts of the body? Are the consequences not from the disease itself, but from the treatment of it, like with chemotherapy and surgery? 

And of course, with illnesses that take place in a magical world, the lasting consequence of contracting the illness could even be that the person is simply blue for the rest of their life, or some part of their body is a different shape. The possibilities are truly limitless. 

Naming Your Fictional Disease

Now for the truly challenging part: naming your fictional disease. There are many different naming conventions for diseases, but there will almost always be an official name and a common name for the same condition. 

Let’s start with the official name.

Sometimes, conditions will be named simply after the pathogen that causes them, such as salmonella.

Other times, they are named after a descriptive plain-English explanation of what the illness does or how it affects someone, such as Acquired Immune Deficiency Syndrome (AIDS) or Severe Acute Respiratory Syndrome (SARS). This option lends itself well to creating an acronym that you can use throughout your story for convenience, as well. 

Another option is to use Greek and Latin roots, suffixes, and prefixes common in the medical lexicon to create a name for your disease. This is definitely the most challenging of the options, but it will often result in the most impressive-sounding names for fictional diseases. Take the word “Hyperthyroidism.” This word can be broken into three parts: “Hyper-” means “higher than normal;” “-thyroid-” obviously means “thyroid gland;” and “-ism” means “relating to.” So the condition can reasonably be inferred to mean “overactive thyroid.”

Another example is Ankylosing Spondylitis—a type of arthritis that causes inflammation in the joints in the spine, and can eventually cause the vertebrae to fuse together. “Ankyl(o)-” means “crooked” or “stiffness;” “-ing” means “action” or “in progress;” “Spondyl(o)-” means “relating to the spine;” and “-itis” means “inflammation.” So putting it all together gives you “inflammation in the spine that gradually results in stiffness or crookedness.” You can use this same process for naming your own fictional disease.

Here’s a List of medical roots, suffixes, and prefixes to help you out! If you choose to use this last option, look up the name you piece together at the end to make sure it isn’t an existing condition already! And, if you need new prefixes and suffixes that aren’t in the medical lexicon, such as words meaning “relating to fae” or “vampires” or something else, you can simply try to find Greek or Latin roots for those words. 

However, people don’t always talk about diseases using their official or scientific names. Sometimes, for example, a disease gets called “swine flu” instead of “H1N1 Influenza.” Diseases are also often named after either the scientist who discovers it, the first person identified with it, or a notable figure who draws attention to it, like Parkinson’s, Treacher Collin’s, and Lou Gehrig’s. Other times, an official name is shortened or abbreviated to make it easier to pronounce and remember. And of course, if a disease comes from space, it’s more likely to be called “alien flu” than anything sophisticated.

In addition to naming your disease, you should also consider coming up with names for medications used to treat the disease. There’s a lot less nuance to this though, since you can simply make up any nonsense word with a few Xs or Zs and no one is going to question it. I mean, take a look at the names for some name-brand medication in the real world: Zyrtec, Tamoxifen, Xgeva, and Incivek. After all, these are brand names, not the technical name of the medicine itself.

This is something that was done quite well in The Fault in Our Stars, in which the protagonist is treated by a drug called “Phalanxifor.”

If you want to name the generic medicine itself, however, here’s another list of suffixes used in medications to help give you an idea of what the different roots mean. 

Know the Relevant Medical Terminology

If you’re going to be writing about diseases, you have to be able to talk about them in a convincing manner. That means you’re going to need to have at least a basic understanding of the terminology surrounding disease and illness, so your readers can take your work seriously. 

I can’t teach you everything, but here are some basic definitions that you inarguable need to know in order to talk about disease—fictional or not:

  • Pathogen – A microorganism that causes disease.
  • Pathogenic Organism – A synonym for pathogen.
  • Host – A cell, creature, plant, or person within which a pathogen lives or multiplies.
  • Bacteria – A type of single-cell organism. Some, but not all, bacteria can cause disease.
  • Virus – A type of infectious, nonliving molecule that contains genetic material. It can multiply within a living cell and spread throughout a body, causing disease.
  • Fungi – A type of spore-producing organism that feeds on organic matter, including mold, mushrooms, and yeast. Some, but not all, fungi can cause illness. 
  • Protozoa – A type of single-cell organism. Some, but not all, protozoa can cause disease. They are distinct from bacteria because they have a nucleus that stores genetic material, whereas bacteria do not.
  • Parasite – An organism that lives on or inside a host creature. The parasite benefits at the host’s expense. 
  • Patient 0 / Patient Zero – A term used to describe the first person identified with a disease at the outbreak of a pandemic.
  • Epidemic – A disease that affects a large number of people within a population.
  • Pandemic – A disease that affects a large number of people across multiple countries or continents. 
  • Endemic – A disease commonly found within a population or particular location.
  • Outbreak – A term used to describe a sudden increase in the incidence of a specific disease.

Ultimately, I can’t list every single term you’re going to need to know. Diseases vary immensely after all, and I can’t predict the kinds of illnesses you’re going to want to create. You will need to be able to do your own research to make sure you are covering the topic in a way that is confident and convincing.

If you need some help getting started, check out my article The 10 Best Ways to Research for a Story

Remember to not get stuck on the details, however. You want to convince readers that you know what you’re talking about, not bore them to death with too much unnecessary medical jargon. 

I hope you found this information helpful! Best of luck with creating your own unique fictional illness to add depth to your worldbuilding!