Help figuring out why my chickens have lost feathers on their underside.

[KariGirl48]

Looking for some assistance with figuring out what is wrong with my hens.
All of my adult hens have lost all of their feathers on their underside around and near their vent. They had lost a few feathers down their last summer, but everything I read suggested it might be due to the hot summer weather here in Florida.
Recently it has gotten worse and now the bare spot has gotten a lot bigger and is now an angry red, which it wasn't before.

This only appears to be affecting my adult hens. My rooster and juvenile (4-5 months old) chickens don't seem to have this problem.
There are no other symptoms. All of my chickens are active, eating properly, laying eggs, and being normal chickens.
Any ideas what is causing this and/or treatment recommendations?

Thanks

 

[cavemanrich]

I would be inclined to suspect mites. They are tiny, and sometimes difficult to spot. No Idea why only your grown hens are the ones affected.
Lets see what others suggest as reason.

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