Have you ever had an intense itch you cannot scratch hard enough to relieve? Occasionally, dogs can experience that too. That said, a dog who frequently scratches, licks or bites at his skin can immediately make us jump to the conclusion the dog has fleas or other pests. While this is one possible explanation for this behavior called "puritus", there are other reasons he may feel the need for a good scratch. Here is a list of common causes of skin irritation in dogs, and how to know when it's time to see the vet.