You may be seeing an allergic reaction to food if this is on the belly area as this is where dogs with food allergies can get rashes. It is not usually a new food that causes this but one the dog has been eating a long time.
food allergies http://www.petplace.com/dogs/food-allergy-in-dogs/page1.aspx
The Golden part of this breed is also prone to Atopy which is from airborne allergies and similar to food allergies. If this is the problem then there is a medicine called atopica to help with this.
Other possibilities are bacterial, fungal, yeast infections or mites . In order to determine this the vet would have to do a skin scraping and this can be done in the office and you will have an answer before you leave. A bacterial infection would require antibiotics for a few weeks and fungal or yeast would require special shampoos, as wold a mite problem. http://www.petplace.com/dogs/skin-scraping/page1.aspx
These are all I could find
mange mites http://community.dog.com/migratedFiles/25849/178E55381CFA4665B5D195D949274644.jpg
Atopy information http://www.lowchensaustralia.com/health/allergic.htm
Bacterial infection (with sun damage) http://www.dermvet.com/index.htm