The mattress has a bad smell.
ma-te-RAS-so — four syllables, stress on the third.
Report this at check-in or at the start of your stay. A smelly mattress is grounds for an immediate room change.
'Ha un cattivo odore' = has a bad smell. Using 'il materasso' (the mattress) rather than just 'la camera' (the room) identifies the specific source of the problem, which helps maintenance act precisely. 'Cattivo' = bad.
Il materasso sa di umido.
The mattress smells of damp.
Specify the type of smell — damp suggests moisture damage
Le lenzuola sembrano non essere state cambiate.
The sheets seem not to have been changed.
A serious hygiene failure — report immediately
Il cuscino ha un odore strano.
The pillow has a strange smell.
Request fresh pillowcases or new pillows
Mattress hygiene is regulated by Italian law — mattresses must be professionally cleaned or replaced on a defined schedule. However, compliance varies. A bad-smelling mattress often indicates a moisture problem in the building, not just poor maintenance. Always report and always accept a room change.