The Vault - Fallout Wiki

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The Vault - Fallout Wiki

Diseases are an integral part of Survival difficulty in Fallout 4.


There is a chance of contracting a disease after eating uncooked meat, drinking unpurified water, taking damage from disease ridden creatures, and using harmful chems; diseases convey a general drawback after contraction. Items the cleanse the body of radiation also come with the side effect of a suppressed immune system, leaving one more vulnerable to contracting a disease. Only one disease (molerat disease) can be obtained outside of Survival difficulty; otherwise, the other six diseases require Survival difficulty being active to contract.

Diseases can be cured by visiting a doctor and paying them to remove it. Alternatively, antibiotics can be used to get rid of diseases. Furthermore, prophylactic herbal remedies can be crafted at chemistry stations to lessen the chances of contracting certain diseases in the first place.



  • The chance for contracting a disease is determined by a roll, depending on the current Disease Risk Pool (DRP). The DRP is a cumulative indicator of the current risk of the character becoming diseased and starts at 0, accumulating percentage points from various environmental and food/drink sources. The DRP decays at a natural rate of -1% per game hour.
  • Sources include:
    • Food always adds +1% to the DRP (but does not force a roll). Foods can also have a low disease risk (+3% to the DRP), standard (+7%), high (+12%), or very high (+20%).
    • Drinking Cola adds +2% to the DRP (does not force a roll).
    • Chems add +7% to the DRP. These include Buffout, Calmex, Daddy-O, Day Tripper, Fury, Jet, Med-X, Mentats, Overdrive, Psycho, and X-Cell.
    • Fighting infected enemies will add +5% to the DRP if hit in combat.
    • Swimming in contaminated water will add +3% to the DRP. The effect stacks every 2.4 game hours (10% of the game day).
    • Exposure to rain adds +3% to the DRP every 12 hours.
  • When the DRP reaches the threshold of 25%, it starts rolling for diseases.
  • All items that cause immunodeficiency add 20% to the global chance to contract disease for the duration of the effect and add a separate +5% to the DRP.
  • If the game rolls a disease, it is added as an effect and the player receives a grace period: They cannot contract another disease for the next 24 hours.


  • When the game rolls for disease, the disease die roll needs to be lower or equal to the current DRP. All diseases have a 5-90% chance of occurring (i.e., the game will randomly select among them to apply it).
  • If the player has taken the appropriate herbal remedy, the value must also be higher than the BoostedImmunityThreshold to get this disease. This number acts as both a minimum Risk Pool threshold to even get this disease and once the Risk Pool is high enough, add some randomness to whether the player gets this disease with each risky action.
  • Every disease has a chance floor and ceiling to be contracted, which will always drain to the floor value.
Disease Effect Herbal remedy
Molerat disease After being bitten by a mole rat in Vault 81, the player permanently suffers from -10 hit points.
Insomnia Sleep is 50% less effective (i.e. you need to sleep at least 4 hours instead of 2 to deal with sleep deprivation) Herbal anodyne
Lethargy Action points regenerate 50% slower Herbal stimulant
Fatigue Sleep deprivation accumulates twice as fast (i.e. the player needs to sleep twice as often) Herbal stimulant
Parasites All food consumed sates just 50% of hunger. Herbal antimicrobial
Weakness All incoming damage is increased by 20% Herbal anodyne
Infection Player takes periodic damage Herbal antimicrobial