The hair transplant donor area is the band of hair around the back and sides of the head, for a man or a woman; an area that is genetically strong and the follicles do not suffer from genetic hair loss properties. Progressive hair loss can mean hair loss drops down the sides and back of the head, extending the surface area of the crown, also known as the vertex; this will potentially eat into the size of the safe zone, especially with FUE.
The FUE technique relies on a wide surface area to extract the hair from as FUE reduces the hair density left in the area; so the wider the area hair can be removed from the lower the density change occurs. The FUT technique, does not require a wide area as the hair is removed in a single strip of hair bearing tissue localised to around 2cm wide around the sides and back, known as the occipital area.
As the FUT donor is located centrally within the overall potential donor zone there is very minimal chance that any hair extracted is unsafe to transplant. Unsafe hair can be miniaturised hair in the donor, this should not be extracted, or even adjacent strong hair and hair outside the safe zone that can suffer from loss in the future.
The safe zone, especially in the early stages of hair loss can be hard to define when using FUE as there are no obvious signs where it may be demarcated; if the lateral humps or crown drop later the safe zone is reduced. FUT relies more on skin laxity when removing the strip, when performed well with good healing a further strip can be removed from the same area, englobing the first line and still reaching high graft numbers.
It helps to shave the donor and measure the FUE safe zone, easier to assess hair qualities and the level of miniaturisation; this is much easier on higher NW cases as there appears an obvious demarcation line. This demarcation line could still drop so it is important to leave a little leeway and not harvest the follicular units directly up to this line; this makes for a more safe an educated harvesting protocol.
As FUE does rely more on a wide surface area, if a candidate has weaker characteristics in the donor it will reduce the total overall FU´s that can safely be extracted; assuming an educated extraction pattern is adhered to. Long term planning is a vital component to the success of the hair transplant, present and in the future; understanding the donor limitations, what each technique is safely capable of and accepting limitations.
This is something that should be discussed prior to any surgical hair restoration because it is not something practical that can be reversed; and regardless of technique there will always be subtle changes to the scalp, donor and recipient