To understand follicular unit, it is better to first know something about anatomy of hair follicle.
Essentially hair follicle is anatomically divided into three regions namely upper or infundibulum, middle or isthmus and lower region. The bottom most part of the hair follicle is the hair bulb, this contains rapidly dividing matrix cells and melanocytes or pigment cells. The dermal papilla and the adjacent matrix are at the bottom of the follicle and in the upper part it consists of hair shaft, inner root sheath, outer root sheath and dermal sheath from inside to outside
What is follicular unit?
It consists of 1-4 terminal hair follicles and one or more vellus hair with its adjacent sebaceous glands, blood vessels, nerves and erector muscle. This follicular integrity is of vital importance in hair transplant and needs to be carefully maintained for hair growth. It is the transplantation of these follicles that had transformed the hair transplant surgery all together. On an average, the density of follicular units in scalp is approximately 80-100 follicular units per square centimeter.
In FUT or strip surgery these follicles should be carefully dissected into individual follicles and should ideally be done under magnification either by good loop or under microscope that too by experienced team to ensure the integrity and hence the viability of hair follicle.
The advantage of using follicular unit in hair transplant is that it gives natural looking hairs when placed in proper direction and at proper angle.
Use of follicular units enables the surgeon to create very small recipient sites. This helps to place more number of follicles in smaller area safely without causing much damage to scalp and without compromising the blood supply of the scalp. If grafts used are larger than the follicular unit than the result will not look natural as the wounds created by larger grafts like in plug transplant or mini/micro grafting may cause lots of cosmetic problem like uneven grafts, dimpling of the grafts, and hypo pigmentation of the areas.
With the use of follicular units, the surgical planning can be done in a better way. The smaller units like those having 1 or 2 hairs can be used in front for hairline and the larger units can be used in the areas behind to provide more central fullness. So one can have better idea of the number of grafts required. Other characteristics which can affect the outcome of hair transplant are color, texture and hair diameter. The thicker the diameter fuller the result.