This is something that can effect item usability apart from its current pristine...damaged...ruined item system. Every item will have a cleanness parameter that will be observable via inspecting.

Examples- a pristine can of bacon in its 'dirty state' will cause sickness due to contamination. A pristine pistol that dirty will be more susceptible to jams and even self destruction.

One good example would be clothes. Damage should only reflect how clothes are torn, and cleanness parameter should reflect how dirty it will look. currently, falling from height and seeing your ruined pants in atrocious state is kinda unrealistic. The cleanness parameters will deteriorate over time, and can be replenished via washing. put dirtied rice in a pot and wash with water for eg.

Character's cleanness parameter will be observable via inventory, and it will effect how a character looks like. A survivor that hasn't washed for weeks will be covered in dust and mud etc. It should also effect the hygiene of the character. Not washing feet that's dirtied with mud may cause you feet infection, not washing body will attract ticks. This may disadvantage a player by excess screen shaking saying 'my body is itchy.'

Cleanness should be something that massively effects survival. This will also boost the importance of medical items in cases of different symptoms caused by bad hygiene.