Dog skin problems

Winter has begun, and I now worry about my dear yellow lab. She often gets big patches on her back (near her hind end) where the fur is just gone, and the skin is bright red. We've tried everything we can think of to help the poor girl. We've changed her food, used topical sprays and creams... we've washed her bedding multiple times, in different detergents... She has no spots right now, but I've found this stuff, Dermaxol, that says it heals these types of skin problems, like "Sores, rashes, eczema, dry/itchy skin or cuts". They say it's all natural. That's good. I'm kind of fussy about that.The weather has been mild so far, and the heater hasn't been on in the basement where she likes to spend most of her time playing, sleeping and hanging out with the other Lab, and bugging B when he works in his workshop. Seems that she hasn't had a skin problem since we got the 2nd lab. Maybe that she was lonely. Poor baby. I used to be with her all the time, but I'm just not another dog! But who knows. It could come back at any time, and I want to be ready. I'll be bookmarking that site for future reference!