In a professional hair iron, a unit (U) is defined by a lower support element (2) and an upper support element (3) hinged together and movable between a rest, open position and an operation, closed position. Complementary facing plates (20, 30, 300, 333) are removably fastened to the support elements (2,3). Heating electric resistors (R) are inserted within the plates and at least one plate of the plates (20, 30, 300, 333) has a perforated portion connected to a supply pipe (C) in turn connected to a steam generator (G) to supply steam to the perforated portion so as to moisten a lock of hair laid between the plates fastened to the support elements (2,3).