All pure bred adult Shih Tzus do have long hair.
If the Shih Tzu you have does not have long hair then it's likely not a pure bred Shih Tzu.
If you have a pure bred and true Shih Tzu it will have long hair to it.
It's OK to shave a Shih Tzu if you want to shave them or need to shave them.
The Shih Tzu will be OK if you do shave them but it's not good to shave the Shih Tzu during the winter or fall months as they can get too cold.
Wait until the warm summer months to shave the Shih Tzu if you need too.
If you cut a Shih Tzu's hair it will take up to 8 weeks for the hair to grow back.
However it may take 6 months for the hair of the Shih Tzu to fully grow back.
The Shih Tzu's hair is usually a bit slow growing at first and then grows back a little faster after it gets near grown back.
But the Shih Tzu should have it's full hair grown back within a year after you cut it or shave it.
If you've shaved the fur off a Shih Tzu it can take from 6 to 8 weeks to start seeing the Shih Tzus fur or hair to grow back.
It can then take a full one year before the Shih Tzu has it's hair fully grown back after shaving or cutting it.
While it's growing out be sure to comb it to help prevent the Shih Tzu's hair from getting tangled.