Doggie Excema? Not a hot spot. Advice?

My 18-month-old havanese has not-a-hot-spot on his thigh. I noticed he was bothering the area about 10 days ago and have kept a careful eye on it daily. He's been bothering it less and less, and he's not chewing or injuring himself as far as I can tell, and it obviously doesn't hurt when I touch or rub it. It's not wet or bright red or anything. BUT, the skin is still reddish and small bits are flaking off. The flakes very small, sort of oval-shaped (but more ragged) with little dots in the middle. I wonder if that's like a scab flaking off (though I didn't see an original injury) or something else.

I clipped away the hair all around so the area can breath, and gave him a lukewarm bath with his fancy hypoallergenic prescription shampoo (he had some topical allergies last fall that went away when I bathed him once a week with the stuff.) The area now looks a lot cleaner.

Anyone ever see anything like this? It seems not to be a huge deal, but it's lasted a while now and would definitely be a big deal if it spread beyond this quarter-sized patch on his thigh. I use frontline and heartguard; he had his yearly checkup and shots and so forth, and I see no evidence of bugs anywhere. Any ideas? Is it time to visit the vet? Etc?