Is there a treatment to grow back hair on vagina?

If you don't have pubic hair, you should see a doctor for an examination. There may be a medical cause.  If there is no medical cause, then hair transplant surgery may be one option to have pubic hair.

In case you don't know what a merkin is, you can look it up.  The permanent alternative to this is pubic hair transplants, a procedure i have performed several times before on women and men.  The main limitation is that the hairs will need to be trimmed moving forward.

This is relatively common for women who do not have pubic hair and want it. We have done many of these pubic hair transplants over the year. 

In Asia pubic hair transplantation is quite common.  Using the Neograft technique the procedure would be minimally invasive with good cosmetic results in most people.