This is a very overlooked area of grooming. If you think about the parts of a Shih Tzu that are most vulnerable to the elements, what would they be? The nose and the paws.
These areas are bombarded with quite a bit.
The nose often gets the full brunt of the sun in the summer. In the winter, noses often get chapped due to cold, dry air.
The paws are subject to walking over all sorts of terrain. In the summer, there are hot surfaces to contend with. In the winter, there is freezing ground surfaces, ice melt chemicals, and snowballing (ice or snow getting wedged in between paw pads or toes).
Year-round, there there are tiny grains of sand which can be quite grating on the paw skin.
If your Shih Tzu's nose looks dry, use a quality nose balm. A good one will both protect the nose and heal any issues (drying, peeling, and even cracking).
To protect your Shih Tzu's paws, you may want to consider using a quality paw wax. This helps provide traction, and adds a breathable layer of protection from every walking surface. If your Shih Tzu has dryness or cracking, or has any damage to the outer layer, a good paw wax will promote healing.