Quantification of normal skin thickness using very high-frequency ultrasound: a clinical study in Chinese adults

Measurement of skin thickness provides an objective basis for diagnosing skin diseases and evaluating treatment efficacy. High-frequency ultrasound (HFUS) offers the advantages of high frequency and resolution, enabling clear visualization of the epidermis, dermis. Very high-frequency ultrasound (VHFUS) boasts an even higher frequency and resolution, allowing for more precise imaging of each skin layer. Both ultrasonic probes with different frequencies can accurately measure skin thickness. The purpose of this study was to compare the differences in skin thickness measured by the above ultrasonic probes in healthy Chinese adults and to analyze the factors influencing skin thickness.

A total of 74 healthy volunteers were included in this cross-sectional study. VHFUS (50 MHz) and HFUS (20 MHz) were used to obtain normal sonographic images of the skin, and the epidermal, dermal, and full-thickness skin thicknesses were measured. We compared the differences in skin thickness measurements between probes of different frequencies, and the differences in VHFUS skin thickness measurements in different sections, left and right sides, sexes, and different parts, and analyzed the relationship between skin thickness measurements and age and body mass index (BMI).

The differences between the epidermal layers of the abdomen (0.1100±0.0178, 0.1097±0.0156 mm; 0.1176±0.0159, 0.1159±0.0158 mm) and chest (0.1039±0.0189, 0.1038±0.0171 mm; 0.1102±0.0169, 0.1134±0.0159 mm) in the longitudinal and transverse sections observed using VHFUS and HFUS were statistically significant (P=0.007, 0.018, 0.034, 0.001). Right and left comparisons of the dermal and full-thickness skin thickness measurements of the forearm (dermal: 1.6138±0.4217, 1.5696±0.3900 mm; full-thickness skin: 1.7324±0.4311, 1.6772±0.3898 mm), and leg (dermal: 1.7977±0.4987, 1.7164±0.4342 mm; full-thickness skin: 1.8964±0.4827, 1.8336±0.4330 mm) show statistically significant differences. Sex comparisons indicated differences in the dermal and full-thickness skin measurements in certain areas (P<0.05). Furthermore, the epidermal layer of the right foot dorsum, dermal layer, and overall skin thickness of the right calf were negatively correlated with age (r=-0.245, -0.229, -0.257). Some dermal and full-thickness skin measurements exhibited weak positive correlations with BMI (r=0.302, 0.306, 0.313, 0.314, 0.300, 0.291, 0.299, 0.302, 0.263, 0.262, 0.255, 0.257). Significant differences in the thicknesses of the skin were observed across various anatomical regions (P<0.05).

VHFUS can obtain clear skin sonograms and accurately measure skin thickness, particularly epidermal thickness. For sites where there is no significant difference in skin thickness between the two sides, the contralateral side can be selected as a reference for unilateral lesions, and age, BMI, and sex impact skin thickness measurement. Different parts of the skin have different thicknesses. Therefore, when measuring skin thickness, it is necessary to establish a corresponding reference range for normal skin thickness based on these influencing factors.