Have his skin issues actually been diagnosed? Have you consulted with your Vet for treatment?
There is a once a month oral medication, Comfortis, you might ask your Vet about. Look it up on the Internet. I know a number of people that use it, ate happy with the results and dogs have had no issues.
However, if your dog is dealing with an immune disorder, best to check with your Vet.
Other than that, try to keep your house and yard treated. You might try getting bedding for him that has Cedar in it.