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and their degree of curliness directly determine the amount of skin that will be hidden by each hair shaft; these characteristics also determine how much or how little skin between individual hairs or grafts is covered.
4,8 A thick, curly hair will hide more skin than a thin, straight one. A tightly curled (kinky) hair will cover the largest area of underlying skin. Similarly, two adjacent curly hairs will mesh and cover the bare skin between them, while adjacent straight hairs behave as individual units covering only the skin that underlies each one.
8 This is demonstrable by comparing the effect of the hair in a person of African descent who has tightly curled hair with that of a blond person of Scandinavian origin.
The African person has a dense carpet of hair that stands up above the scalp while the Scandinavian’s hair lies close to the scalp and barely hides the skin when the hair is wet. Yet, a count of the actual number of hairs per square millimeter may show that the African person has many fewer hairs than the Scandinavian.9
The contrast between the color of skin and the color of hair is also critical to the ability of hair to cover the underlying skin. Tanned skin and blond or light brown hair blend, so that visible skin is not obvious;
covering the pale white skin of a person with sparse, coarse, black hair such that the graft looks natural is a surgical challenge.1 This applies also when considering the thickness of individual hair shafts and their relationship to hairs in proximity to other hairs of the same character.
The contrast between coarse, black hairs and a pale, white skin accentuates a “clumpy” appearance if present. In order to achieve a fully natural appearance, the spaces between the grafts must be filled with small minigrafts and one or two hair micrografts, especially in the hairline.8
If the Scandinavian described above has a dense hair population, the large number of hairs and the small size of the spaces between hairs will combine to lend body to the mass-until male pattern baldness sets in.
With our method of measurement, hair density ranges between 1.2 and 3 hairs/mm2. A traditional, 4-mm round graft contains almost 13 mm2 of skin surface area.6
The number of transplanted hairs in a graft is directly proportional to the surface area of the graft and to the density of the hair in the donor area. The density of the permanent hair in the donor area should be the baseline for this measurement.
A true evaluation of the transplantation process requires assessment of the number of hairs per unit area in the donor site, in order to obtain predictable results. The need to assess donor hair density is less apparent with 4-mm grafts than with minigrafts. In many cases, this may be purely a mathematical issue.
The loss of two hairs from a graft that originally contained 24 hairs represents an 8 percent reduction; this would not be noticeable unless an exact hair count had been done before and after grafting. T
he loss of two hairs from a graft that originally contained four hairs would represent a 50 percent reduction which would be obvious to all. Moreover, comparison between transplantation of donor grafts with two hairs /mm2 and one of donor grafts with 1.3 hairs/mm2 would show a dramatic difference.
In order to accurately assess the number of hairs per unit area in the donor area and the grafts, we developed a device to measure hair density. We believe that this measurement is critical to obtaining predictable, high quality results with minigrafts.
to our surprise, that our keen “surgical eyes” were less accurate than we had presumed, for determining hair density. The difference in results when density was directly measured quickly became obvious.
We found that a minigraft containing four hairs offers the best combination of body and invisibility for a person with dark, coarse, straight hair;
while a person whose hair is light, thin, and straight can support grafts with a larger hair population without looking “pluggy.” This holds for most areas of the scalp except for the frontal hairline where smaller grafts are necessary.
The decision to use a 1.5- or 2-mm graft is based on the surgeon’s assessment of the patient’s hair density, color, texture, and character. If calculations suggest that a 1.5-mm graft is needed to produce four hairs per graft in a person with coarse, black, straight hair and pale, white skin, then a 1.5-mm graft should be used.
A 2-mm graft in such an individual will increase the density of hair by 30 percent and will increase the visual “plugginess.”