Tear Staining

Tear staining is a common problem in Maltese.  Tear staining is the reddish brown discoloration that is found on the hair under the eyes.  It occurs in other breeds as well, but with the white face, does make it show up more in the Maltese.
Tear staining is caused by excessive tear production (epiphora).  The hair under the eyes is constantly wet and this can lead to it staining.
One interesting fact is if there is no excessive tearing, there will be no tear staining.  It's also not unusual to have littermates---one who stains and one who doesn't.  Genetics does play a role in tear staining.

First and foremost, it is very important to see your vet or ophthalmologist first to rule out any medical causes for excessive tearing.  ***This can't be stressed enough.
Some medical causes include:  ingrown eyelashes, infection of the eye, unusually large tear glands,  unusually small or blocked tear ducts, glaucoma,  entropion (inverted eyelid),  large prominent eyes, ear infection, dental issues, some kind of systemic issue and certain medications.

There are other elements that can cause excessive tearing:  stress, hormonal changes, higher humidity, smog, high winds, allergens, irritants, second hand smoke, plastic food/water bowls, high mineral content of water, allergies, type of food fed, hair in the eyes and teething.

As you can see, there are many possible reasons for excessive tearing.

Tear stains are usually the result of porphyrins.  Porphyrins are iron containing molecules that are produced when the body breaks down red blood cells.  Some of these porphyrins are excreted through tears, saliva and the pads of the feet.
When tears containing porphyrins sit on the hair for any period of time, staining will occur.  And yes, the iron related stains will darken if exposed to sunlight.

Besides porphyrins, red yeast (Pityrosporum) can also contribute to tear staining.  Yeast loves moist areas, so wet hair under the eyes would certainly be favourable for it to flourish.  Yeast infection under the eyes will have a noticeable odour.
It is quite possible for a dog to have both porphyrins and yeast at the same time.

To add to the confusion, bacteria seem to be involved somehow.  The mechanism of bacteria is not well understood.  What is clear is that some dogs who are given certain antibiotics will result in the tear staining clearing up.

So what to do?
Once the vet has ruled out any medical issues, there are a number of things you can try to reduce the staining:
--Keep the facial hair clean and dry.  This may require tending to the wet area 2-3 times a day.  Avoid using commercial liquid products.  You want to keep the area dry, not wet.
Use a flea comb to remove any eye debris and blot with a tissue.
A favourite recipe is to take a pinch of half cornstarch/half boric acid powder and work it into the wet hair with your fingers, then leave it. The cornstarch helps dry the area while the boric acid will gradually lighten the staining. If you do this diligently every day, usually within a month, you can see a noticeable change. 
--Try changing the diet.  Food allergies can contribute to staining.
--Adding a probiotic may be of benefit
--Use glass or stainless steel food dishes.  Plastic dishes can harbour bacteria.  Many breeders use "water bottles" to help keep the faces dry.
--Try distilled or filtered water instead of tap water
--For pets, trim the hair at the corner of the eyes.  It helps prevent the tears from "wicking" down the moustache.
--For some, flushing the eyes daily with an eyewash containing boric acid eg. Collyrium can help
--If the tear ducts are plugged, your vet might be able to flush them out.  Be aware however, that this is often a temporary measure, as the ducts often plug up again with time.
--Air filters or air purifiers can be helpful
Just to mention, Tums, apple cider vinegar and buttermilk have been "said" to change the pH of the tears.  There is little evidence to show this is the case and results are very variable.

Last but not least is going the antibiotic route.  This is something that should not be taken lightly.  Antibiotic resistance is becoming a huge problem in the world.
If all of the above has failed, then perhaps trying a course of antibiotics might be worth looking into.
You and your vet will have to work together on to figure out the correct dosage and for how long. 
Tylan (tylosin) seems to be the drug of choice these days.
Antibiotics for tear staining doesn't work on all dogs, so if the staining isn't clearing up after a reasonable length of time, don't continue using it.
Likewise, an antibiotic may work, but you can't keep them on it for a long length of time either.

As you might gather, there is no magic wand for stopping tear staining.   Every dog is different, but with perseverance, it should be possible to get staining down to a minimum.