Brian replies: THE symptoms that [...].
It is almost certainly an allergic response that is causing mild skin irritation for your pet, hence the licking.
When I do allergy tests to diagnose these, I find more than 95 per cent of reactions are caused by either flea saliva or house dust mite sensitivity.
You haven't seen anything because you are not able to see house mites with the naked eye.
It is possible to de-sensitise your pet to these allergies using a specially made course of immunotherapy, which I have found very effective, even with my own cat.