Difficulty is a feature in Plague Inc. and Plague Inc: Evolved that alters gameplay according to difficulty. Note that if you beat a plague on any difficulty except casual, the all the easier difficulties on the scenario or plague type will have be beaten, as well. For example, if you beat a plague or scenario on brutal, then the difficulties of normal and casual will have be beaten as well.
Casual is the easiest difficulty, and is for those wanting a quick or easy game. In it people are extremely careless, and do not wash their hands. Doctors don't work, and sick people are even given hugs.
"For new players or those wanting a quick game"
- No one washes their hands - Normal infection rates.
- Research doctors don't work - Slow cure research.
- Sick people given hugs - Increased infectivity.
Normal is the average difficulty, and is the minimum for unlocking the next (standard) plague type. In this difficulty, more people wash their hands, as well as doctors contributing to research."For experienced genetic strategists"
- 67.3% of people wash hands - Infectivity decreased.
- Doctors work 3 days a week - Cure developed at average speeds.
- Sick people ignored - Infectivity decreased once spotted.
Brutal is the second hardest difficulty, and was the hardest before Mega Brutal was introduced. Brutal introduces obstacles such as excessive hand washing, very determined doctors, and higher disease paranoia. Winning with all standard plague types unlocks the Neurax Worm, and winning with the Neurax Worm on Brutal unlocks Necroa Virus and so on."For strategic geniuses living in concrete bunkers"
- Compulsive hand washing - Infection rates decreased dramatically.
- Doctors never go home - Cure research is much faster than Normal.
- Sick people locked in prison - When disease is spotted, infection rates are greatly lowered.
Mega Brutal is the hardest difficulty of all. Introduced with Plague Inc: Evolved and later added in the Mutation 8 update for the mobile Plague Inc., this difficulty can be slightly slower, and doctors may discover a disease with no symptoms. Doctors will, even then, stop at nothing to cure diseases."For players who thought Brutal was Casual!"
- Genetic drift impacts evolution - Symptom costs fluctuate over time, generally becoming more expensive with more people infected. Vice versa, lowering the amount of infected humans will reduce the genetic drift penalty cost.
- Doctors invest in research - Fastest cure research speed.
- Random medical check ups - Plague will randomly be detected through "Anomalous blood test results" that usually happen a month or two after the country is infected. Detection chance is related to how many people are infected. Country wealth seems to play a role as well. Unlike other difficulties, the pathogen will be easier to detect once the population in a country reaches critical mass as opposed to the severity.
- Completing a game in casual difficulty will not unlock a new plague, unlike the other difficulties. It will instead unlock new genes.