A. Very common condition, usually cause by either yeast or bacterias (could also be ear mites). It's treated with special antifungal/antibiotic ear drops which contains steroids as well to stop the itchiness.
In some cases systemic antibiotics are require as well, treatment length depends on severity and causative agent, usually between 1-3 weeks.
Any vet can help you with this, you just need to make an appointment and get your shitzu checked.
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