Itchy behind ears

Not mites or fleas, and driving my poor cat nuts, I was wondering if anyone has ever encountered this ? Nothing visible, no bites, maybe a sinus thing, or like a fool I start thinking tumour, cancer....

My guess would go towards food.

I would go with food allergy or possibly a litter allergy.  Have you recently changed his food or litter?

Vague, but I'll try. Litter rarely get used, but cared for a young female for a week, who used the box. I'll turf that. Eats the same thing all the time, Purina Cat Chow. Hasn't bothered him for 12 years. Gets a treat of a spoonful of Friskies can catfood frequently....

Can't get a better answer unless you give something more descriptive. Like the flavor is almost more important than the brand when it comes to allergies  

Same food for 12 years, do allergies start that randomly ?

I do thank you for your input, and do IIntend to try any and all suggestions.

* intend

Cat and dog food makers will change their ingredients from time to time, it happens with a lot of brands. But it's important to know what flavor it is. Like chicken,tuna,salmon,lamb,rabbit, etc... 

Yes, regarding the food allergies. Oftentimes it happens that way, the cat develops an allergy to a food that has been given for a long period of time.

Another thing that seems to really be a source of allergies is any product made with corn or other grains.

Hope this gives you a starting point.