SKIN ISSUES
A major complaint is Hot Spots in Shih-Tzu due to feeding SOY and other 
allergens. GOOD FOOD is essential in shih-tzu. They tend to have very sensitive stomachs. If they vomit green, it's BILE, and you need to change food to an easier-digested food, such as LAMB and RICE.
If your dog has skin issues like scaly patches, it could be ringworm and can be deadly to people on chemotherapy. Antifungal shampoo and salve will help clear it. Ringworm is carried by cats. 
Lamb and Rice feed is a good start to see if your dogs hot spots are due to a food allergy. It can take up to six weeks to start clearing once you change feed. We found Salmon and rice are very good for coat problems.
The Omega 3's help in the salmon. Too much O3 can cause diarrhea if you use fish oil on their food. 
I NEVER buy Chinese imported treats or toys either. The pieces of rubber may be ingested with toxic poisons.
DO NOT feed FAT, bacon, meat scraps table scraps or you risk pancreatitis. 
Many foods cause BLADDER STONES. Use a food recommended by the BREEDER, not your vet, under
normal circumstances.  I have a hate list of brands of food for shih-tzu due to problems that arose due to feed. 
 

We feed Nutrisource and Tuffy's Gold (sold at Menards and made by Nutri Source, but less expensive). 
Puppies get Nutri Source Puppy food. SEE Nutrisourcepetfoods.com for dealer locations. 
WE NEVER FEED ROYAL CANINE OR SCIENCE DIET TO SHIH-TZU. Our experience is death and stomach issues.