Dogs pant because of heat, nervousness or illness, according to petMD. As dogs cannot sweat through the skin like humans do, they circulate cool air through their bodies by panting. Many dogs pant when they get nervous or excited, such as when a thunderstorm is near. Panting may also indicate heart or respiratory problems, along with several other diseases.
A dog's body temperature can rise quickly when it is hot outside. The thick coat prevents cooling of the body by sweating, though some sweating does occur on the pads of the feet. Opening the mouth to pant allows the dog to bring cooler air into the body and expel the warmer air. Panting also intensifies during exercise as the dog's body heats up rapidly due to the increased physical effort. A fresh supply of water can help the dog stay hydrated and cool down during exercise and hot weather.
Loud noises and unexpected flashes of light can scare a dog. When lightning or a thunderstorm occurs, many dogs cower and seek cover. Panting while hiding from the storm is common and is a side effect of this nervousness. Calming the dog generally stops the excessive panting.
Recurring panting with no apparent cause may indicate the presence of disease, such pneumonia, in the dog. Pet owners should watch for other signs of illness to confirm suspicions and seek the advice of a competent veterinarian if the symptoms persist.