Hi Johnn,
Have you gotten hold of your rooster to look and see if he might have mites or lice? You would need to look way down under the feathers, next to the skin. The vent area is a good place to look, and also under the wings.....
If you see any critters, then buy some Seven Dust, and give him a good dusting. The whole flock may require it. Then you repeat in 14 days, because the eggs will hatch and then you'll need to kill the baby lice/mites before the are mature enough to lay more eggs and repeat the cycle.
Usually the skin is not bright red, so I'm guessing it's a parasite problem.