What could be causing dog's hair to turn black and fall out?
We recently adopted a dog and I have noticed several small bald spots in his skin. It looks like the hairs, not the skin, are turning black and falling out. I'm not sure that these spot haven't been there a while and I'm just now noticing them. The skin that is revealed is pink, but the hair follicles under the skin look black. He eats, drinks, sleeps, plays etc normally. The spots don't seem to itch him, he doesn't bother them. Any ideas?
I called the vet when I saw the first one. She and I agreed it wasn't ringworm because no one else in the house has it, we have 2 humans, 2 cats, 2 dogs. I also don't think it's thyroid, because, again, no other symptoms. No excessive drinking, no bloating etc... Any other thoughts?
ETA The vet didn't think I needed to bring him in unless it got worse or they seemed to bother him.