Filth and Contamination Rules


Plague Doctor from Darkest Dungeon

Adventurers delve down into filth and blood all the time, fighting through slimes and oozes in dank sewers. We like to think being dirty is no big deal for the grim and hardened, but filth comes with the potential for disease and even the most hardened can fall prey to the psychological trauma of perpetual filthiness. My Low Road game has also forced me to come up with rules for dealing with more volatile contaminants.

This also gives the potential to do a filth based dungeon: like a sewer crawl where wading through filth and fighting monsters comes with the additional hazard of managing your filth levels.

Filth: Everyone has a Filth Save starting at 15. Everyone has a Filth Threshold equal to their Con score.

Each time a PC is exposed to Filth, they must make a Filth Save. This only happens once per Turn of exposure. Filth functions like damage where each example of Filth has its own Filth Die. Examples follow:

1d4: Wading through ankle-deep sewers. Killing or being within 5ft of the killing of 1-3 enemies in melee combat. Breathing in a potent odor.

1d6: Wading through knee-high sewers. Killing or being within 5ft of the killing of 4-6 enemies in melee combat. Being attacked by a small muck golem or an ooze. Breathing in an overwhelming odor.

1d8:  Waist-high sewers. 7-10 enemies. Each round spent submerged in a non-acidic ooze. Falling in a pile of refuse. Being attacked by a larger muck creature or ooze. Breathing in the worst smell ever.

1d10: Swimming through sewer water. 11+ enemies. Being stuck in a mucus pod or cocoon or vat of slime. 

If Filth should ever meet or exceed the Threshold, roll on the table below. Every time the PC's Filth increases over or beyond the Threshold, roll again.

1d12 Dirty Consequences:
  1. Roll on your Disease table of choice. It begins to manifest in 1d4 days.
  2. Roll on your Mutation table of choice. It begins to manifest in 1d4 days.
  3. Roll on your Madness table of choice.
  4. Wounds become infected. If you are below max HP or take damage before you are cleaned. Unless you are treated with alcohol or thoroughly get your wounds cleaned within 1d4 days, a random limb will start to necrotize and it will have to be amputated. 
  5. Armor begins to degrade. -1 AC.
  6. Protective Clothing begins to degrade. +1 to Save and -1 to Threshold bonus.
  7. The mind turns inward to endure against the filth. -2 (+2 to roll under) to all rolls requiring mental ability or fortitude. Spells have a 1 in 4 chance of failing. You cannot prepare spells. Lasts until cleaned.
  8. Quaking and weakness afflict you. -2 (+2 to roll under) to all rolls requiring physical fortitude or force. -2 Max HP. -1 to melee damage. Lasts until you are cleaned.
  9. Slickness makes it difficult to find your footing. -2 (+2 to roll under) to all rolls requiring balance and coordination. -2 to AC. until you are cleaned.
  10. During your next stressful occasion (Combat, encountering a trap, ect) you are afflicted with constant vomiting. Save vs Poison each round or get -5 (+5 to roll under) to rolls and AC (If Ascending) until the situation is resolved.
  11. Food doesn't stay down. Use starvation rules. Lasts until cleaned.
  12. Your smell begins to attract attention. Roll two encounter checks instead of one whenever you would roll them. Lasts until cleaned.
Cleaning Filth is not as easy as it might sound. First off, leaving a filthy area is going to be necessary. If you are already filthy and surrounded by filth, a quick splash of water will do little to relieve you. If you are in a filthy area like a dungeon or the sewers, there is little you can do to clean yourself without magic. If you should find yourself in a place of clean reprieve in the middle of a filthy dungeon, using up 1 Item Slot worth of water and soap per Turn will reduce your filth by Soap Die+1 per Turn spent cleaning. If this cleaning reduces your Filth below your Threshold, any ongoing impermanent Dirty Consequence will cease unless your Filth rises above the Threshold once more before you have been completely cleaned, in which case, all Consequences will resume.

A good bath at an inn and a clean set of clothes reduces your Filth to 0. All clothes and armor must also be washed and oiled as necessary or, Filth is only reduced by half and all clothes have a 1 in 3 chance of being permanently damaged. (-1 AC/+1 Save, -1Threshold.)

Protective Clothing can decrease your Save and Increase your Threshold.

Protective Clothing: (Using Lamentations Silver Standard + Ascending AC)
  • Poor Quality: -3 to Save, +3 to Threshold: 100 sp
  • Middling Quality: -5 to Save, +5 to Threshold: +2 AC, 200 sp
  • Excellent Quality: -8 to Save, +8 to Threshold: +3, AC, 500 sp
  • Protection Addition to Armor: -5 to Save, +5 to Threshold, +1,000 sp to the cost of any armor.
Umbrella: Can protect against contaminants falling from above. -2 to Save where the protection is possible but not absolute. 50 sp.

Arm-High Gloves: Let's you touch contaminants and filth without taking ill effects. -2 to Save where protection is possible but not absolute. 10sp. (All Protective Clothing ought to automatically be assumed to come with gloves such as these, and it is already factored into their Save Bonuses. This entry is in case a PC doesn't want to wear the full outfit.)

Knee-High Boots/Any kind of Leather Overalls: -2 to Saves for wading through up to knee-high filth. 15sp. (All Protective Clothing ought to automatically be assumed to come with these, and it is already factored into their Save Bonuses. This entry is in case a PC doesn't want to wear the full outfit.)

Perfume Sprayer/Incense Censer/Thurible: -5 to Saves against gaseous filth such as noxious fumes and sewer stank. Costs 150 sp, 50sp for each Hour of uses.

Soap: Soap in medieval times was a little different from how we tend to think of soap. Soap is an ancient invention, going back all the way to the Babylonians, but nicely prepared soap tends to be quite expensive. The most common method of cleaning your hands was to dip them in a little wood ash and wash them in water. Other soaps were made from ash and animal fats or, more expensively,  olive oil. See this fantastic video for more information here.
  • Wood Ash: 2cp, 1d4 Soap Die
  • Black Soap: 10sp, 1d6 Soap Die
  • Grey Soap: 50 sp, 1d8 Soap Die
  • Castile Soap: 100sp, 1d10 Soap Die

Contaminants: More potent contaminants, such as radioactive or infectious materials can also be simulated by altering the Save and Threshold depending on the situation. Walking headfirst into radioactive death-snow ought to automatically harm someone unless they have some kind of protection, but where such protection might be questionable, Filth rules can help.

For instance, say the PCs were to walk into an area where it was raining some kind of poison ooze. The PCs are smart enough to not walk right in so they invest in some protective clothing, however, the ooze builds up as they are in it, making it possible the clothing will not protect them forever.

In this case, I set the base Threshold at 5 modified by protective clothing and Con mod, and keep the base Contamination Save at 15. If the amount of Contamination should meet or exceed a PC's Threshold, they are affected by the specific effect of the ooze.

PCs should be made aware of these rules if they are entering into this sort of scenario to ensure they understand the risks and can take proper precautions. 


  1. On the one hand, I generally appreciate unique stress systems, particularly when they fit thematically with the setting and have interesting consequences. On the other hand, in some ways this seems like it should fall under Constitution or Poison Save or something along those lines (depending on system). Given that "Filth" in this context is something a little more symbolic it's by no means a critical flaw, but I do think it should be made clear within the text or in play what is "mundane filth" vs. "Filth".

    1. I am not talking about supernatural filth so much as I am talking about just a lot of mundane filth. In this case, I don't think it makes sense to do a Poison Save. Your physical hardiness doesn't stop you from getting dirty. It can help you endure it, as I have done with the Con score equaling your Threshold, but it doesn't really make sense to me for this sort of save to be modified by anything other than the kind of protection you use.

      I will say, I don't think these rules ought to be dumped into just any game. I am making them in preparation for an idea I had for a sewer dungeon all about being as dirty as possible, full of oozes and muck monsters.

      I think it could make for some interesting choices. One way in waist high sewer water but otherwise clear while the other way is clean but trapped or has monsters. Also adding a further detriment to combat in the form of blood-splatter increasing Filth, adds an extra layer of decision making.

    2. Aah, I don't think I processed the part about the Con score equaling threshold, I think that makes sense and is in-line with what I was looking for.

      In regards to the "mundane filth" vs. "Filth", I don't necessarily mean that "Filth" has to be supernatural. I just mean that it is something of thematic importance to the setting, or has some symbolic value. Particularly, in a system that is not so much trying to be "Simulationist", I think adding a mechanic such as this is saying, in this system/setting, Filth is an important aspect of this world / unique thing to contend with. Con is still a factor in determining effects of Filth, which I think is still appropriate, but Filth is something more than just a single attribute roll or save roll with a quantitative or single categorical effect.

      These kinds of specific, targeted, thematic game mechanics are something I've been very interested in lately. I agree that while theoretically it could be thrown in other games, I think it makes more sense to have it in a game with only a few other of these kinds of specific mechanics, that all evoke a particular theme.

  2. Funky foulness that I definetly gave to incoporate into my grotty campaign rules. I've been struggling to figure out how to make clothing somethin g worth paying attention to outisde of fighting the cold and this does it for me.


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