My dog has red circles on his under side, legs/arm pit area, not raised or swollen but smooth what could it be?

I’ve only seen it once when I was a little kid… but uh…. sounds like ringworm. There’s docs on here who can tell you more, but you might want to google pictures of Ringworm and see if that looks like it.

if it is ringworm you’d better be careful any other animals can get it and so can you.

Sounds like ringworm to me as well. @delirium, you beat me to it!

Could also possibly be some type of allergic reaction. Is your dog licking or scratching at it?

Sorry I just noticed that you wrote that he is licking it…Have you recently changed anything in the house or has he been anywhere where the grass has bee sprayed with chemicals? Ringworm is a possibility. I would take him to your vet and have him checked out. If it is ringworm it is contagious.

It could be ringworm – if you tug on the hair at the periphery of the lesion, does it come out easily?

The more common condition is a staph or other bacterial infection. Usually they’re itchy or uncomfortable, have roundish lesions with flaky skin, and the dog usually smells bad.

It doesn’t sound typical, but with skin conditions you always have to consider the possibility of sarcoptic or demodectic mange.

All of the above conditions require a trip to your veterinarian for treatment.