Since your dog is unable to communicate with you, the best way to tell if something is bothering them is having to watch their behavior. A lot of people don't know that panting could be a sign that something's wrong. Here are some reason's why I don't like seeing your dog pant.
Overheating. Remember they are wearing fur coats and many of our companion dogs are overweight. Sometimes we have dogs that evolved in arctic climates e.g. Huskies and they are not well adapted to Summers in warmer regions. Some people shave down their dogs in the warm months, when actually they should be “stripped” down so that the guard hairs remain for dissipating heat but the downy undercoat is removed. Some dogs who are shaved can actually overheat and can get sunburned. Very few professional dog groomers know how to perform this type of procedure. It requires certain grooming tools such as combs with clipper-like teeth. Some groomers that treat show dogs of certain breeds “strip” the coats regularly.
Anxiety. Nervousness. Reactivity and other behavioral issues.
Overstimulation. Even if your dog is happy sometimes there are too much stimuli and it can be overwhelming to your pet. Inevitably this type of panting will occur, but it should not be sustained because of negative stress hormones such as Epinepherine, Cortisol, glucocorticoids, catecholamines, thyroid hormones, etc. can have deleterious effects.
Possible underlying diseases. Hyperadrenocorticism (Cushing’s Disease), Diabetes Mellitus, Diabetes Insipidus, Heart disease, Lung disease, cancer, and Cognitive Dysfunction Syndrome are common causes of panting due to disease.
Medications. Certain medications can cause panting or cause increased body temperature e.g. Prednisone.