I Don’t Understand Donor Hair Supply Limits

Sorry for my ignorance on the matter but I’m a little confused.

I have heard people mention donor hair running out. Why is this exactly? If it is immune to balding, why can’t you harvest an unlimited supply from it to transplant?

Once hair is removed from the donor area to be placed elsewhere in the scalp, it does not regrow in the donor. So let’s look at the numbers….

If we take the most advanced balding pattern, for example, the patient having lost most of his non-permanent hair will have 25% of the original hair left. That would be 25,000 hairs, or 12,500 follicular units. If you need to keep 66% of this permanent hair, that means that you can harvest 8,250 grafts in a person with a birth hair population of 100,000 (Caucasians are good examples of this). This assumes medium hair thickness

Taking more than 8,250 follicular units as two hair grafts might leave you donor depleted. This is especially true if you are Asian, Indian or come from the Middle-east where birth hair numbers often run 80,000-90,000 birth hairs or the hair is fine.