If your dog is experiencing skin-related rashes, there are several reasons that those rashes may be occurring. Luckily, with almost every cause there's a form of treatment that can be taken to cure the rashes that occur.
Evaluate your dogs' environment. If there has been any changes in where they walk, where they choose to lie down or any other changes, it's important to note those circumstances. Some dogs can develop allergies and you can eliminate their rashes if you can isolate what that allergy may be and then removing them from that environment.
Give your dog omega-3 fatty acids. You can find these fatty acids in wet and hard dog food, however, for maximum dosages a teaspoon of the actual oil is recommended on a daily basis. You can find one form of the liquid in the "Additional Resources" link at the bottom of this page. Omega-3 fatty acids can help prevent against inflammation and allergens, which can help reduce rashes from occurring.
Apply a flea and tick collar or, more effectively, an application of medicine such as Frontline. This is not only smart for helping rashes but also for protecting the health of your dog.
Use dog shampoo and conditioner. You can purchase pet shampoos at most pet supply stores. This can help remove any irritants that may be on your pet's skin. Applying a fresh coat of soap and conditioner once a week can help reduce allergens that make their way onto your dog's skin.
Give your dog a small dose of Benadryl. This can help ease minor allergies and thus reduce your dog's rash by helping it to stop itching.
Try a home remedy by applying around one to two tablespoons of olive oil to your dog's food; it can help alleviate any itching and rashes.