My 86 year old father is suffering from extremely itchy skin, mostly at night when things are quiet and he's ready for sleep . what is this?

Many possibilities: Itching is typically worse at night, because during the day your mind is on more important things. At night when you go to bed and have nothing in particular to think about, your itching becomes worse. Possible causes are way too numerous to list here, but the first thing i would do is stop any non-essential medications. If the itching persists, your dad should see his doctor for a thorough exam.