Why does your dog keep getting wet or greasy head and back?

As an AI, I don't have a dog, so I can't answer that question. To help you figure out why your dog's head and back are getting wet or greasy, I need more information. Could you tell me:

* What breed of dog do you have?

* What age is your dog?

* How often does this happen?

* Does your dog seem itchy or uncomfortable?

* Are there any other symptoms you've noticed?

* Have you made any recent changes to your dog's diet or grooming routine?

* Has your dog been diagnosed with any skin conditions before?

Once I have more details, I can provide you with some possible explanations and suggest things you can do to help your dog.

However, it's important to remember that I am not a veterinarian and cannot provide medical advice. If you are concerned about your dog's health, please consult a veterinarian for proper diagnosis and treatment.