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INTRODUCTION
Skin thickness can vary widely among
individuals as a result of a person’s gender, age, and location. In order to
measure skin thickness, a variety of tools have been used. Scanning electron
microscopy and light microscopy have been used to measure thickness of skin in
vitro [1]. To measure the thickness of the skin in vivo, a skin caliper
instrument can be used, however, it is less commonly used today as it is not a
precise measurement [2]. A method that has been shown to be a reliable direct
measure of unmodified skin is ultrasound scanning, a non- invasive method for
in vivo measurement of epidermal and dermal thickness [3]. There are two types
of ultrasonography including A and B mode, as well as different frequencies
that can be used. The dermis and hypodermis is measured well with 20MHz
ultrasound, but the epidermis is much thinner indicating that HFUS up to 100MHz
should be used to better visualize the epidermis [4]. The purpose of this
review is to understand the factors that influence skin thickness and echo
density.
Factors Influencing
Skin Thickness and Echo Density
Skin thickness and echo density can be
influenced by factors such as increasing age, gender, and particular sites of
the body. Evidence suggests that skin thickness is typically higher in males
than females, opposite of echo density, which is typically higher in women
[1,5-7]. Gender, however, has not been shown to play a significant role in
epidermal entrance echo thickness [1]. Although age was not reported to affect
echo density [1], age is a significant factor in skin thickness.
Thickness of the dermis is more often thinner in the aging population
[1,5,6,8-10].
To gain a better understanding of these influencing
factors, this review will focus on the study “The influence of gender and age
on the thickness and echo-density of skin”, while also reviewing other articles
in the literature that analyze skin measurements. Firooz et al. used high frequency
ultrasonography (HFUS) to assess influencing factors such as gender, age, and
location on skin to further determine how these variables affect skin thickness
and echo density of skin [1]. Epidermal entrance echo thickness, dermal
thickness, and echo density of dermis was measured in 30 individuals, 17 female
and 13 male. With the use of B mode HFUS at 22 and 50MHz ultrasonic probes,
five anatomic locations were measured, and healthy participants were placed
into groups based on age. The age range was 24- 61 years old; the young skin
group consisted of subjects less than 35 years old and the old skin group
consisted of subjects over 35 years old. Subjects were not included in the
study if they met any of the following exclusion criteria: any skin disorders,
application of corticosteroid drugs, BMI >30, chronic systemic diseases,
instant sun exposure in previous 3 months and/or hard physical activity.
The five skin locations measured included the cheek,
neck, palm, dorsum of the foot, and sole. The study was done in winter to avoid
exposure to sun in subjects over the previous 3 months due to the fact that sun
exposed areas have less decrease in skin thickness compared to protected areas
[11].
Firooz et al. found that dermal thickness was higher
in males compared to females, showing statistical significance on the neck and
dorsum of foot. Shuster et al. also showed thickness of dermis in all ages was
higher in men than women in the forearm [5]. Furthermore, a 25 MHz A mode
ultrasonography used to measure the ventral forearm of 54 men and 64 women
between ages 0-90+ years of age concluded that in all ages, the skin thickness
of men was higher than women’s skin thickness (p<0.001).6Because
different sites of the body were measured and different tools were used, the
studies suggest that there is strong evidence that men have a thicker dermis
than women overall.
Epidermal entrance echo thickness was also
measured with the use of B mode HFUS indicating that it is higher in men than
women; however, it did not reach statistical significance in any site [1]. Echo
thickness was almost equal in men and women in the dorsum of the foot. All the
information regarding epidermal entrance echo thickness is based on the
findings of Firooz et al. There is limited amount of information on epidermal
entrance echo thickness due to the fact that it may not be commonly measured.
Lastly, echo density of dermis was found to
be higher in females on all sites, showing significance on the neck only [1].
Similar to epidermal entrance echo thickness, the echo density on the dorsum of
the foot was almost equal in men and women. When comparing age groups, however,
there was no significant difference in echo density.
Supporting these findings, Seidenari et al.
concluded that echo density of dermis was higher in women than men using a
20MHz B-mode scanner [7]. Skin thickness and echo density of dermis was
analyzed on six sites of 48 individuals divided into two groups each with 27
subjects, from 27-31 years of age and over 60 years of age respectively. This
same study also concluded that skin thickness on the forehead, cheek, volar
forearm, dorsal forearm, and upper abdomen was higher in males compared to
females [7].
Different locations on the body also
influence skin measurements. Taking the overall mean of all the sites measured,
Firooz et al. reported that the palm had the thickest dermis, the sole had the
highest epidermal entrance echo, and the neck showed the highest echo density
of dermis [1]. This may be a result of different sites receiving more sun
exposure than others or an individual’s amount of activity.
Comparison between the two age groups found
that epidermal entrance echo thickness and thickness of dermis in the young age
group was higher than the old age group [1]. Epidermal entrance echo thickness
decreased with age on the palm, cheek, and dorsum of the foot, however, it was only
significantly higher in young adults on the dorsum of the foot. It remained
constant on the neck and sole. Thickness of the dermis was statistically higher
in young adults in the sole [1].
It was also shown that skin thickness decreased with age. Branchet et al. concluded that in both men and women, epidermal thickness decreased with age after analyzing the skin of 34 women and 30 men between 20- 80 years of age. The study showed that skin thickness in men decreased 7.2% per decade, which was more significant, than in women with a 5.7% decrease per decade [8]. Other studies suggested that age related thinning of the skin was more prominent in women [6,9]. Thinning of the skin can begin as early as the third and fourth decade of life. 8,9Shuster et al. found that skin thickness in females was shown to be constant until the age of 40, and then began decreasing with age (p<0.001). With increasing age, the skin thickness of men gradually decreased (
Using 25MHz B- mode ultrasound, images were
obtained from 142 women with 10-20 subjects in each decade of lie from 0-90
years old. De Rigal et al. showed that the skin on the volar forearm of women
mostly thinned after the eighth decade (p<0.05), without showing significant
variations between the first and seventh decade of life (p<0.001) [10].
However, Escoffier et al. showed that subjects under 15 years old had thinner
skin, but their skin thickness actually increased between 0 and 20-30 years
(p<0.013) with no variation between 15-65 years of age. Skin thickness was significantly thinner in
subjects after 65 years of age [6]. Slight differences in findings between De
Rigal et al. and Escoffier et al. could be associated to the use of B mode and
A mode devices respectively.
Other studies found no significant difference
between age groups. Using 25MHz ultrasound and confocal microscopy, dermis
thickness on the back of the arm was measured in females, 16 women 18-25 years
old and 18 women 62-69 years old. The thickness of the living epidermis was
lower in aged subjects; however, there was no significant difference between
the young group (15 ± 3 um) and aged group (17 ± 3um) [12]. Sauerman et al.
also found no correlation between whole skin thickness and age with the use of
confocal microscopy [13].
The images from HUFS include the epidermal
entrance echo, dermal layer, and echogenic subcutaneous tissue. The
echogenicity of the epidermis is affected by the content of keratin, collagen
in the dermis, and fat lobules in the subcutaneous tissue [14]. Some studies
suggest that echogenicity increases with age [15], while others report
echogenicity of the dermis decreases with age [16-19]. These differences in
results might be explained by the changes that occur with aging such as
decreased elasticity of the skin that may affect dermal echogenicity as well as
skin thickness [20,21].
CONCLUSION
Epidermal and dermal thickness varies depending on
many factors such as gender, location, and sun exposure. 22 This
could attribute to the varied results in the literature. Environmental factors
as well as hormonal status among individuals should also be taken into
consideration. Body sites and population could also account for other
differences between studies. It was noted that high frequency ultrasonography
is an accurate tool for skin thickness measurements, density, and echogenicity
of the dermis. In addition to analyzing larger sample sizes and standardizing
conditions, the use of ultrasonography for skin measurements could be a
beneficial tool for future research.
1. Firooz A,
Rajabi-Estarabadi A, Zartab H, Pazhohi N, Fanian F, Janani L (2017) The
influence of gender and age on the thickness and echo-density of skin. Skin Res
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2. Agache P (2004) Metrology of the stratum
corneum: Measuring the skin. Springer-Verlag, Berlin.
3. Payne PA (1985) Medical and industrial
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4. Aspres N, Egerton IB, Lim AC, Shumack SP
(2003) Imaging the skin. Australas J Dermatol 44: 19-27.
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6. Escoffier C, de Rigal J, Rochefort A,
Vasselet R, Leveque JL, Agache PG (1989) Age-related mechanical properties of
human skin: an in vivo study. J Invest Dermatol 93: 353-357.
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Giannetti A (1994) Echographic evaluation with image analysis of normal skin:
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AM (1990) Skin thickness changes in normal aging skin. Gerontol 36: 28-35.
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(2002) Age related changes of human skin investigated with histometric
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15. Pellacani G, Seidenari S (1999)
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Venereol 79: 366-369.
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irritancy: measurement of skin fold thickness. Contact Dermatitis 9: 21-26.
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microscopy. J Invest Dermatol 88(3 Suppl): 44s-51s.
18. Ritz-Timme S, Laumeier I, Collins MJ
(2003) Aspartic acid racemization: evidence for marked longevity of elastin in
human skin. Br J Dermatol 149: 951-959.
19. Nouveau-Richard S, Monot M, Bastien P, de
Lacharriere O (2004) In vivo epidermal thickness measurement: ultrasound vs.
confocal imaging. Skin Res Technol 10: 136-140.
20. Malm M, Samman M, Serup J (1995) In vivo
skin elasticity of 22 anatomical sites: The vertical gradient of skin extensibility
and implications in gravitational aging. Skin Res Technol 1: 61-67.
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body region. Sci World J 386936.
22. Whitton JT, Everall JD (1972) Epidermal
and dermal thickness. Br J Radiol 45: 611-612.
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