Because of the chemical nature of impulse and the axon-dendrite structure. Because of the chemical nature of impulse and the axon-dendrite structure. http://www.biologymad.com/nervoussystem/nerveimpulses.htm (Best technical explanation and excellent graphics and animations)
Newborns may sneeze, and this is typically attributed to the irritation of their nasal passages. The most common irritants, explains Dr. Iannelli, are smoke (and simply smoking outside is not enough), animal dander from pets in the house, dust mites, and mold.
Fundamentally, a sneeze is a way the body removes inflammation and congestion from the nasal passages. Much like a cough keeps the airways clear, a sneeze is a reflex to keep the nasal passages clear. As such, sneezing after meals suggests that there is some cause of inflammation that occurs after each meal. As for what is causing the inflammation, you are right in thinking allergies are the most common cause. Common food allergies such as egg, peanut, etc should be ruled out.