What's going on?
Licks are one way that canines express their love and fondness for their humans. So, licks really are the canine equivalent of a kiss.
And in general, human skin actually gives off a good taste to dogs, due to salts (sodium, chloride, and potassium) that are left on the skin once perspiration evaporates.
However, while it's nice to get a lick every now and then, if your Shih Tzu won't stop licking you, no doubt you've realized how much of a problem this can become.
Most licking issues start because an innocent lick is given...and then, due to an owner's reaction, the taste of the salty skin on a dog's tongue, or both, a Shih Tzu may become obsessive about this.
How to stop this:
First, for a Shih Tzu to stop licking you, your dog needs to understand what a lick is. Then, you can train your Shih Tzu that not licking you is beneficial and the better choice.