Yeah, ritual impurity is forgotten in modern West and hard to describe to a modern non-religious person.

It is not the same as "being unhygienic", though it overlaps to some degree. (Faeces etc.)

An interesting example from Judaism is "Tzaraath", which means skin disease, but it could also afflict houses. Today we do not know for sure what it even meant. Mold infestation? Maybe.

https://en.wikipedia.org/wiki/Tzaraath#Affliction_of_housing