Not all hotels hold the same standards when it comes to the cleanliness of their rooms.

A recent study by hotels.info found Rio de Janeiro, Brazil, has the dirtiest hotels.

The worldwide online reservation service asks guests who booked with them to evaluate their stay on criteria such as value, room quality, friendliness/competence of staff, and, of course, the cleanliness of the room.

The site recommends customers complain about shortcomings of hotel cleanliness to the local representative or hotel management in a "polite but firm" manner.

Rio de Janeiro received a score of 7.29/10 for cleanliness, with London and Oslo, Norway, just ahead of it in cleanliness.

Tokyo hotels are the cleanest, according to hotels.info, scoring an 8.93/10.