Hair Transplant Coverage and Density
Written by Hair Transplant Surgeon Ali Emre Karadeniz
Publish Date: 25.04.2019
Patients frequently ask "I want it all covered" or "How much can you cover?". You have to always keep in mind that there are two aspects of a hair transplant: coverage and density, and they are opposite.
Our topic is "hair transplant coverage and density" which is a very critical issue and is frequently asked. I'll try to give you a general overview.
If you look at the natural density of the scalp, you will see that it is different from patient to patient or ethnicity to ethnicity. You'll see on average a follicular unit density of around 80 follicular units per square centimeter. This correlates to approximately 200 hairs per square centimeter of an area. We start realizing that our hair is thinning when we are close to 50 percent of our original density. That means from the 200 or 250 hairs that we actually have we start realizing we are thinning when we reach a hair loss of a hundred hairs. That means the hair starts becoming see-through.
If you look at hair transplant densities, the highest transplanted density is around 50% of original density. This is like the difference between natural rainforest which the trees actually grow from the soil with the pollens distributed, the plants will grow so thickly that you may find that even light doesn't pass through these trees. If you want to make a garden and you plant mature trees you can't do it like a rainforest, you'll bring mature trees and you'll dig holes that are a couple of meters apart. If you do them so closely together most often they will hit each other and they will not survive, their roots will damage each other, you have to put a certain distance. Hair transplants are similar, because we dig in a hole surgically and we bring a mature hair to put in, the density we can do and those technical limitations is on average 50 percent original density. But thank God that 50 percent looks very close to native density, if we can get 50 percent - that's a hundred hairs per square centimeter or a little bit above that - this will mimic very close natural density, we call this "cosmetic density" because mathematically that's only 50 percent but visually it looks close to normal.
So we have to know this limitation, this limitation also becomes an advantage because that means when we harvest donor hairs we can cover a bigger area than these hairs would actually cover in nature. Patients frequently ask "I want it all covered" or "How much can you cover?". The problem here is that you can actually cover with any given hair number or a graft number, you can cover an area that you want provided that you reduce the density. If the density is not determined, then we don't know how much this will cover. There will be a significant difference of coverage depending on how much density you try to put in. Professional clinics will usually try to prioritize density, so they will do a much smaller area than unprofessional clinics and give a high density in that region and then in another surgical they'll try to fix another area. Unprofessional clinics - because it's much easier to do - will generally spread out in a whole area evenly the hairs that they harvest because it's much easier to technically do.
Patients tend to go for a surgeon or a clinic that offers more coverage but they don't realize you can increase the area of coverage by reducing density. So if you don't know which density they're going to operate at, then knowing the coverage doesn't mean anything, you have to know both of these factors.
Hair transplants are very labor intensive procedures and I'll give you a general idea about the coverage or density you can expect. FUE is a frequently used technique. In FUE if you harvest around 5,000 hairs and depending on the hair per graft ratio this could be anywhere between 1,700 to 2,500 grafts. It takes the surgical team of a surgeon and perhaps 2 or 3 assistants, it takes 6 to 8 hours, so it takes a full day. In one surgical day you're going to do approximately five thousand hairs or around 2,000 grafts, roughly speaking. If you want to give a good density you must put 100 hairs per square centimeter, so if you put a hundred hairs - or you could put even more - then 5,000 hairs is going to cover an area that is 50 square centimeters. 50 square centimeters is like a 7x7 cm., in general that's like the frontal region or can be the crown, it's an area like this. In a very bald person the recipient area may be up to 200 square centimeters. If you multiply that by a 100, you may realize that this would take up to 20,000 hairs to cover with a good density which is never possible with a single surgical session and single method. A surgical session, a reasonable session in FUE or strip surgery (FUT) is going to give about 5,000 hairs, 2,000 – 2,500 grafts. A very large session is going to give you 3,000 – 4,000 grafts perhaps, and perhaps 8,000 – 10,000 hairs. So you're looking roughly between 5,000 in a normal session or 8,000 – 10,000 in a huge session, mind you in FUE we would do that in two surgical sessions most of the time, because you can't do that much in one session.
But even if you do 10,000 hairs, that's actually a 100 square centimeters of coverage, so unfortunately in hair transplants there's a lot of work to be done, let's say cover-up a moderate region with good density. Of course if you sacrifice density then you can cover a huge area. Therefore, you have to always keep in mind that there are two aspects of this: coverage and density, and they are opposite. The more coverage the less density, the more density the less coverage, so you have to realize this two sides of the scale.
I hope I was able to give you a general idea about how density issues work in the native density, the hair loss density, the transplanted density and the rough relationship between all these three.
Written By Dr. Ali Emre Karadeniz, MD, PhD
Ali Emre Karadeniz, MD (Dr. K) is the only American Board of Hair Restoration Surgery Certified Turkish plastic surgeon. He has performed over 2000 hair operations. He is an active member of the International Society of Hair Restoration Surgery (ISHRS).