The authors agree that Carosio is a surname characteristic of the Alessandria area and the Genoa area, with presence in the regions of Piedmont and Liguria; they note that the surname would derive from the medieval name Carosius. Rossoni specifies that this name is documented from the 16th century, which allows it to be classified as a patronymic, that is, a surname formed from the name of the ancestor.

Carosio belongs to a group of phonetically similar surnames —such as Caruso, Carosi, Carosso or Caroselli— that, despite their similarities, do not necessarily share the same origin. Some of them derive from the Sicilian dialectal term caruso ("boy, apprentice"), others from place names or nicknames linked to agricultural activities. Carosio, on the other hand, is distinguished by its medieval onomastic base and its geographical rooting in the northwest of Italy.