No, it is not irreversible, there are many things you can do to replenish your gut flora.
I find it so frustrating looking at this thread and seeing people going on and on about topical chemicals. These cannot solve the problem, plain and simple they're band aids. It stems from internal imbalances so treat it at the source
The only thing that has a chance of long lasting results are fecal transplants, which are progressing at lightning speeds due to their efficacy over all medical Rx's.