Although I’ve never heard of any long-term permanent damage from doing the Master Cleanse, I have seen reports on my Master Cleanse Forum from a very few women who did a Master Cleanse each month for three months in a row and had temporary hair loss.
I believe it is due to mineral deficiency. So, I tell people to wait 3 or 4 months between cleanses and be sure to eat lots of fresh green leafy vegetables like spinach, lettuce, green smoothies, etc. to rebuild their alkaline minerals (calcium, magnesium, potassium and sodium).
It may also be a result of going beyond a clear pink tongue or the return of hunger for healthy food (not cravings for junk) as signs the cleanse is complete.
Interestingly, I’ve never heard this happening to anyone who does one long MC regardless of length nor have I ever heard this happening to a man!