Mutation

Mutation is a concept not found in the vanilla game (as of alpha 12.3). The mutation debuff uses the same symbol as infection in your character window but is a different condition. In Barinou's mod infection can be cured with antibiotics as in the vanilla game. Mutation, however, can only be cured by finding a very rare secret on the corpse of one of the big bosses. Until that happens, mutation causes the player's max health to decrease slowly but relentlessly.

Don't make the mistake of trying to cure mutation with many antibiotic pills, because taking more than 3 antibiotic pills within a day-and-a-half period will lead to a weakness debuff.