I don't know what causes your dog's skin problem but mine is due to environmental cause. My dogs started to have skin problem after we moved house two years ago and so we thought it's the new cement that caused it. We didn't know why the problem persisted after more than a year until we stopped using bleach and floor detergent to wash the back court about 6 months ago. We used to wash the back court heavily with the detergent at least once a week to get rid of the rabbit urine stain on the court where my bunny barn sat. Although we made sure we'd used enough water to flush the detergent before we allowed our dogs to enter the area, the detergent did cause the skin problem of my dogs. After we use plain water to use the area every day, we start to see the improvement after a few months and now their skin is fully recovered. Hope it's of reference to you.

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Grandma