A hair transplant is a fantastic way to regain the look of a full head of hair, but is also a long-term task, and it is important to understand the terminology associated with hair transplantation.
In order to gain objective information you need to deal with the facts and it is important to clarify the terminology in advance, especially as many are internationally recognised to set a reasonable basis of understanding.
Follicular Unit – a consistent name
A follicular unit (FU) is a naturally intact group of follicles/hairs growing together, normally from 1 to 4 hairs, on occasion 5 hair groupings with an average of 2.2 hairs per grouping. Here several hair shafts each with their own root grow together to form a “bundle” known as hair follicular units (FU = eng.Follicular units).
Each follicular unit has its own sebaceous gland and muscle attachments, they are surrounded by blood vessels, nerve fibres and collagen binding. The phrase follicular unit (FU) has established itself internationally as a recognised term to describe the grouping; this is important as some marketing will use terms such as mini graft, micro graft, or simply a graft which do not necessarily constitute a natural FU.
Mathematical aesthetic density versus density
It is very important to understand what is the natural hair density and what is required with a hair transplant to give a natural looking hair density.
Around the scalp the hair groupings (FU) grow in varying densities; the back of the head can have a natural density around 70-90 FUcm² while the sides generally slightly lower, 60-70 FUcm². Although there is a density difference between the sides and the back the eye does not necessarily recognise this because there is adequate scalp coverage despite a lower mathematical density.
As long as there is sufficient to hair of sufficient quality over an area to block the incident light there can be a lower density and still achieve the desired result. With the miniaturisation of the hair shaft a loss of coverage quality can arise without a strong mathematical decreased in actual density of hair. So there is a difference between mathematical and aesthetic density.
A hair transplant can never create 100% density again but with technical and artistic finesse in the redistribution of permanent donor hair an aesthetic density and coverage can be achieved. This is a mathematical relationship between the size of the surface area to be covered and the number, quality and hair characteristics of the donor hair.
Read here , about the hair transplant techniques