Your father is an elderly diabetic and suffering from renal insufficiency
He complains of itching in whole of his body.
Due to impaired renal function the toxic end products which has to be excreted by the kidney
gets accumulates in the body. This produces generalized itching.
This end products are also excreted in the sweat in the form of salts.
The deposition of his excess salts also causes itching.
Advice regular bathing.
Other treatment a symptomatic.