Hills Prescription Diet Derm Defense has been specially designed for dogs who suffer from environmental sensitivities. There are many environmental factors that affect our pets each and every day including fleas, pollen and even the dust in our homes. For some dogs these irritants can cause a skin condition that may lead to scratching. This is unpleasant for your dog and can also be difficult for everyone else in the family! The good news is, most dogs with these skin conditions can benefit simply from the right food.