There's an awful lot of mis-information out there on the subject of tear staining (particularly in small white dog breeds) which can lead to the situation not being dealt with properly.
Finding sensible advice and info is not easy, but I've done my best and am indebted to the website of Indianapolis veterinarian Greg Magnusson DVM.
One of the problems is exemplified by a leaflet I picked up recently on the subject, which fails to mention any underlying health problems, focussing mainly on a range of possible 'toxins' and blaming poor quality diet - which seems to be a bit of an over-simplification of the problem, its causes and possible treatment (but good marketing of course!)
Some dogs seem more prone to this problem than others. Over generations of breeding, we have turned wolves into Bichons, poodles, Maltese and a wide range of breeds with shorter noses than their ancestors and a tendency for protruding eyes. These will naturally contribute to a narrowing and sometimes crooked tear ducts. There's not a lot that can be done for these dogs - we've bred them that way !
There are also medical or vetinary causes of excess tearing, including ingrown eye lashes, abnormally large tear glands or small tear duct openings. Add to these stress, medication, poor diet, ear infections, and yeast infections causing brown discolouration and owners should really ask their veterinarian for advice before doing anything else!
The toxins, if that's what you want to call them, are porphyrins, which are iron-containing molecules, hence the reddish-brown discolouration - they are produced when the body breaks down red blood cells and would normally be excreted the normal way through the gut.
In some dogs, however the porphyrins are excreted through urine, saliva and tears, and if they stay on the fur for a significant amount of time they will stain it. That's why it's not only around the eyes that the problem is apparent - it can show where the dog has been licking, i.e. after licking paws clean.
A bacterial overload or inbalance can also potentially be a cause of excessive production of porphyrins. This was discovered when antibiotic treatment was discovered to eliminate the problem in a few but not all dogs.
As mentioned, a small percentage of cases seem to respond to antibiotics. There are supplements advertised that may help, but should be used with care as any substance you add to a dog's diet is potentially a toxin!
Veterinarian Greg Magnusson DVM recommends the following sensible approach
1) Clean your dog's face regularly with a damp cloth, and keep the dog regularly groomed.
2) Use stainless steel food bowls because cracks inplastic ones can harbour harmful bacteria that might be associated with this problem.
3) If your tap water is high in minerals then switch to using bottled water for your dog's bowl.
4) Use a high quality natural diet, whichever one works for your dog, no one is better than another. There does seem to be consensus that poor diet can increase production of porphyrins.
For the whole article go to http://www.leospetcare.com/a-veterinary-guide-to-tear-stains/