The authors agree that the surname has a toponymic origin, although they differ as to the geographical referents and the proposed etymologies. One of the referents is the place name Cairo Montenotte, whose etymology is attributed to the Latin gentilic Carius or to the Latin adjective quadrus, "square".

F. Miranda broadens the picture and identifies multiple independent clusters of origin arisen in different regions without direct relation to each other. The northern cluster would derive from place names such as Pieve del Cairo and Cairo Lomellina, in the province of Pavia, and Cairo Montenotte, in the province of Savona; in this case, the etymological base would be the medieval Latin cairum, with a root in the Old Ligurian car, "stone or rock". Miranda adds that the surname is present in western Lombardy and eastern Piedmont, with extension to Calabria, Puglia, Lazio, Campania, Liguria, Emilia-Romagna, Tuscany, Veneto and Sicily.

For the southern clusters, Miranda proposes two hypotheses: that they derive from the Norman name Chair or, according to other scholars, from the Arabic term hair, "kind, good". In Sicily, the surname appears in the Syracuse, Catania and Enna areas.