I'm only answering this based on experience. It's caused by water or food drying on their face. Because this breed has such a short and flat face topped by long facial hairs, when food and water dries up it leaves a "dirty-mop" smell. I trimmed my dogs facial hair and used a hanging water bottle (similar to that used for hamsters. Hope this helps.
Shih Tzus are generally from Japan!
The Shih Tzus nickname is "The lion dog".
Shih Tzus are primarily used as Companion Dogs.
Some shih-tzus have cherry eyes. My shih tzu has one.
Black Shih Tzus are not considered "Rare" but there not as common as the black and white Shih Tzus. I recommend this breed to anyone.
Shih tzus can live with any dog as long as there not vicious, and are socialised properly.
Shih tzus weigh 9 to 16 lbs. I have two Shihtzus and they both weigh 14lbs.
Why Yes They Do
no
Just like your question, both of the male shih tzus are the fathers.
Because as puppies there hair on their face look like a chrysanthemum flower.
Shih tzus do NOT shed.