Why Does My Cat Keep Scratching His Ear?

[JodyBuchanan]

For a few months now, my big orange cat has been scratching his right ear. It's not all the time, but when he does start scratching, he really goes at it. He tries to dig in there and I can tell that something is really bothering him. Because of this, I began cleaning his ears with Excel Ear Cleaning Pads, which has helped get some of the gunk out. The stuff that's left on the pads is brown. Like a brown smear.

I've also been putting a few drops of Otic Enzymatic Solution by Zymox (ear drops) every day. I did that for a week. He stopped scratching for a while, but it seems like he's starting back up again. It's not as bad this time around, but I really don't want his to have to scratch at all.

When I look inside his ears, I can see that the canal is sort of dirty. The dirt is really far down there though, not on the outside at all.

My question is, what's in his ears that's making him scratch? It is mites? I don't think it is because I've treated him with Revolution (Stonghold) and that is supposed to get rid of ear mites. Is it a fungus? Bacteria? Yeast? Or just wax buildup? I'm also wondering if it may be a food allergy or a general allergy. I read online that cat allergies can make them scratch their ears.

Does anyone have any experience with this? If so, can you please share?

Thanks!