Dogs sneeze when they are excited to communicate to their playmates that their interaction is just play, or simply to let another animal or human know that they want to play. The play sneeze, or excited sneeze, is a way for a dog to convey his intentions to those around it.
While there are many factors than can cause a dog to sneeze, such as allergies and irritation, the sneezes associated with these conditions are readily identifiable. Most notably, these other types of sneezing are accompanied by other symptoms, such as scratching, unusual mucus discharge or even fever. The sounds of the sneezes are much different as well, with the playful sneeze often repeated several times and ejecting mostly air, cleanly and unobstructed.
According the Canine University, many dogs that lack sufficient socializing with other canines often display this type of behavior at the first sign of another dog or person, regardless of the energy level of the other. This is where normal, playful behavior becomes problematic, as it is often followed by jumping, pawing and even fighting with other dogs. This is where exposure to other, well-behaved dogs, along with diligence from the owner, play important roles in the overall behavior of each individual animal.