During my daily meandering through online forums, I picked up an interesting question from a perplexed dog owner. This one relates to a natural phenomenon called tear stains.
The concerned dog owner asked what causes a tear stain and if it was true that changing dog food brands causes it. First of all, anyone involved in dog ownership, or in the appreciation of this wonderful branch of the animal kingdom, is not new to the sight of a tearful dog. Sure, but they are not tears of sorrow but an overflow of this liquid whose function is to clean the eyeballs. There are ducts that allow this liquid to drain into the nasal area where it is eliminated. When these ducts are clogged or closed, for whatever reason, the liquid overflows unto the cheek area and causes the stain that we are so familiar with. Many small dogs, like Chihuahuas, have protruding eyeballs. Tear staining is very common among them as well as in any toy class. In this case, the protrusion of the eyeballs stretches the ducts and prohibits the liquid from draining into the nasal cavity. Humans are no different. Ever wonder why our noses clog up when we cry? Excessive tearing, thus crying, causes an overload in the nasal cavity even if tears are overflowing unto our cheeks. That's when we reach for the tissue. For goodness sake, when you see these tears, please do not assume that the dog is emotionally distressed neither is it overjoyed.
As for changing dog food brands as the possible culprit, it seems to me that someone was trying a different angle on this issue, one with commercial interest.