One of our dogs developed this, in exactly the same places as your cat. As a user of herbal and natural remedies, I was tempted to bathe the areas in something like aloe vera, but our vet said just to leave it, in case the animal scratched the area and the preparations stung.
The hair grew back slightly, but not overly so, so we've just left it, and put it down to the dog geting older. She's now 7, and has had this thing for about 2 years. It doesn't bother her at all, and she's an otherwise very healthy dog with a shiny coat.