Variations of Hair Follicle Size and Distribution in Different Body Sites

Abstract

For the evaluation and quantification of follicular penetration processes, the knowledge of variations of hair follicle parameters in different body sites is basic. Characteristics of follicle sizes and potential follicular reservoir were determined in cyanoacrylate skin surface biopsies, taken from seven different skin areas (lateral forehead, back, thorax, upper arm, forearm, thigh, and calf region). The highest hair follicle density and percentage of follicular orifices on the skin surface and infundibular surface were found on the forehead, whereas the highest average size of the follicular orifices was measured in the calf region. The highest infundibular volume and therefore a potential follicular reservoir was calculated for the forehead and for the calf region, although the calf region showed the lowest hair follicle density. The calculated follicular volume of these two skin areas was as high as the estimated reservoir of the stratum corneum. The lowest values for every other parameter were found on the forearm. The present investigation clearly contradicts former hypothesis that the amount of appendages of the total skin surface represents not more than 0.1%. Every body region disposes its own hair follicle characteristics, which, in the future, should lead us to a differential evaluation of skin penetration processes and a completely different understanding of penetration of topically applied drugs and cosmetics.

Effective use of transdermal drug delivery in children

“…in contrast, in adults, the corresponding values on the occipital scalp have been measured to be only 239 and 292-455 per cm 2 [49][50][51]. The hair follicle density in adults is significantly lower (14-90 follicles.cm -2 ) at other body sites, but comparable values are not available for new-borns [50].…”

“…The hair follicle density in adults is significantly lower (14-90 follicles.cm -2 ) at other body sites, but comparable values are not available for new-borns [50]. More recently, video-dermatoscopy was used to characterize five areas of the scalp in 45 neonates, and identified that two clinical patterns, namely "good hair density" (GHD) and "poor hair density" (PHD) can be present at birth.…”

Recently identified features that help to distinguish ceremonial tsantsa from commercial shrunken heads

“…This includes the fine, peachwhite hypopigmented, nonmedullated vellus hairs that ordinarily cover most of the body and constitute facial down. The facial skin presents a remarkably elevated concentration of follicles in the postcranial anatomy, especially across the nose [25,26,27]. In living subjects, only 2-3mm of the vellus hair is exposed on the skin surface [28].…”

Cutaneous malignant melanoma incidences analyzed worldwide by skin type over advancing age of males and females: Evidence estrogen and androgenic hair are risk factors

“…One can obtain some support for this idea by comparing the distribution of CMM with the distribution of androgenic body hair over male and female body sites. Males have more hair that is androgenic on their face, neck, and torso while females have more hair that is androgenic on their lower limbs [21] coincident with the body sites CMM is found most frequently. [22] Because outdoor workers have a lower CMM incidence than indoor workers, [17] yet they get three to ten times the annual UV radiation (UVR; 290 nm -400 nm) dose that indoor workers get, [23] we know the cumulative dose of UVR is not involved in CMM.…”