The health of a dog is based on a lot of factors including genetics, exercise, and regular checkups, to name a few. But the number one factor affecting the health of a dog is the kind of food that it consumes. There are many types of commercial dog foods and diets on the market today, from BARF (bones and raw food), to steam-extruded products.
Get to know your pet food labels (K9 Magazine has an excellent feature on this subject).
Read the label and avoid products with chemicals and un-natural additives.
You will likely avoid allergic reactions and skin problems in your dog.