missing feathers

[homegrown]

I have 5 hens, but 1 is starting to miss some feathers around her butt. She has plenty of energy and doesn't appear as if it bothers her. Is this a sign of mites? I've looked and don't see any, but I may be missing them. What is the best way to dust my hens, and is it OK to dust them for preventive measures?
Thanks for any advise.

 

[EngieKisses]

Do you have an overly active or aggressive roo?

 

[homegrown]

No, i don't have a roo. Was thinking about getting one so I can raise my own chicks, instead of buying them. Want to increase my flock this year. Meat and more layers.

 

[debilou]

Hi, I also have a hen who has been sporting a thinner and thinner amount of fluff on her butt, for about a month I think. At first I was just thinking it was part of molting, but now all the hens are fully covered except for Louise's butt. Additionally, the skin that's showing looks quite red. I change the hay/shavings in their house every few days, so there are no moist or dirty places where she would be sitting. The hens peck at each other sometimes, but there are only three of them and she is actually the most aggressive.
Does this sound like it requires action?