Differences in Epidermal Thickness Observed in Healthy Skin

Jan Kottner, PhD

A new investigation from Berlin detailed differences in epidermal thickness (ET) in healthy adults based on age, skin type, and ethnic origin.

Skin diseases such as psoriasis and atopic dermatitis are defined by epidermal alterations that affect epidermal thickness. Investigators cited ongoing debates regarding possible ET differences between skin areas, age groups, sexes, phototypes, and ethnic origins.

Despite light microscopy being considered the common method for conducting ET measurements, comparisons between in-vivo measurement methods or to histology are limited.

As such, investigators led by Jan Kottner, PhD, Charité University of Medicine in Berlin, conducted a systematic review that summarized the empirical evidence about ET in healthy individuals, compared the results of different measurement methods and investigated the potential influence of age, sex, skin phototype and ethnic origin.

Kottner and colleagues included randomized controlled trials, observational studies, and other experimental studies if they met the study’s inclusion criteria.

Inclusion criteria involved primary research reports, reporting of ET estimates, reporting of measurement methods, reporting of measured skin area, clear reporting of age and optional reporting of sex, and measurements being conducted on normal, intact, and disease-free human skin.

After establishing inclusion criteria, the team performed combined search of the Medline and Embase databases via OvidSP. The database search spanned 1946 to June 3, 2020.

During the database search, several in-vivo and ex-vivo techniques for defining epidermal thickness were found, and data were extracted on light microscopy, OCT, high-frequency US, multiphoton laser tomography (MLT), and laser scanning microscopy (LSM).

Skin area-specific estimates were also extracted from individual studies and were summarized into broader skin areas when feasible.

Notably, multiple definitions of ET were found in the literature seatch, with some studies having unclear definitions. The main summary measure was the mean ET per skin area in micrometers.

After the exclusion of duplicate studies and title-abstract screening, a total of 431 publications were retrieved for full-text study. Of these publications, 142 were included in the qualitative synthesis, and data from 133 studies were included in the meta-analysis.

Investigators noted that all reported ET estimates were categorized into 37 skin areas including the genitals (11) to the volar forearm (980).

The lowest ET was reported for the penis (31.2(95%CI27.8to 34.6) μm) and the highest for the plant araspect of the foot(596.6(95%CI443.9to 749.3) μm).

With the exception of high-frequency US, the differences in epidermal thickness among the reported methods were minor. In 5 skin areas, however, the difference was statistically significant.

Regarding different ethnic origins, the highest ET was calculated for Asian skin at the forehead (93.1 (95% CI 85.8 to 100.5) μm) and lowest ET for African skin (50.0 (95% 47.5 to 52.5) μm)at the dorsal forearm.

White skin was always lower compared to both Black and Asian skin, with the exception of the dorsal forearm.

Finally, VET estimates were provided for 21 anatomical sites, with the lowest values of 51.5 (95% CI 48.6 to 54.4) μm and52.7(95%CI38.6,66.9)μm) being observed at the axilla and the periorbital areas, respectively.

Meanwhile, the highest values of 520.0 (95% CI 239.5 to 800.5) μm and 182.9 (95% CI 25.8 to 340.0) μm in the fingertip and the palm.

“These values can be used for study planning, and understanding of skin diseases, and the influence of intrinsic and extrinsic factors on the skin,” the team wrote.

The study, "Epidermal thickness in healthy humans: A systematic review and meta-analysis," was published online in JEADV.