Association of facial skin thickness measured by ultrasound with skin type, gender, age, and body mass index

This study aimed to determine the thickness of facial skin layers (epidermis, dermis, total skin, and hypodermis) in adults using ultrasonography and to investigate the association of these measurements with demographic and clinical variables such as age, sex, body mass index and Fitzpatrick skin type, as well as with various lifestyle habits, including water consumption, smoking, caffeine intake, exercise, sleep position, and sun exposure. In this prospective cross-sectional study, 128 healthy volunteers aged 18-65 were evaluated. For each participant, the thicknesses of the epidermis, dermis, total skin, and hypodermis were measured via ultrasonography at 12 distinct anatomical sites, including the forehead, glabella, nose, chin, bilateral temporal regions, bilateral nasolabial folds, bilateral cheeks, and bilateral upper eyelids. Statistical analysis involved parametric and non-parametric tests, along with multiple comparison analyses (p < 0,05 was considered significant). As expected, the lowest thickness for all layers was measured in the inherently thin eyelid, followed by the forehead and nose. The epidermis was the thickest in the chin region, the dermis and total skin were the thickest at the nose, and the hypodermis was the thickest in the cheek. In males, the epidermis, dermis, and total skin were significantly thicker than those in females, whereas the hypodermal thickness was greater in females. The mean hypodermal thickness was higher in the < 30 age group; however, no significant age-related differences were detected in the epidermal and dermal thicknesses. The dermis and total skin were thicker in the 25-29,99 kg/m² body mass index group than in the normal-weight group, while hypodermal thickness was greatest in the obese (> 30 kg/m²) group compared with all other groups. The dermis was significantly thicker in individuals with Fitzpatrick Type 4 skin compared with Types 2-3. Participants who consumed > 14 glasses of water per day had greater dermal and total skin thickness than those who consumed < 7 glasses. A significant difference in hypodermal thickness was found between the groups smoking < 10 and 11-20 cigarettes/day, although a dose-response correlation was not observed. Dermal and total skin thickness were significantly greater in individuals consuming > 500 mg/day of caffeine. In supine sleepers, midline facial epidermal and total skin thicknesses were greater than in those who slept on their right side. The effects of regular exercise, sunscreen use, ultraviolet exposure, and alcohol consumption on mean thickness were either borderline or statistically insignificant. The data obtained via ultrasonography revealed the heterogeneous nature of facial skin thickness, which varies depending on the region, sex, and anthropometric variables. The observation of a thicker epidermis and dermis in males and a thicker hypodermis in females can inform the planning of injection depths in aesthetic and reconstructive procedures. The effects of body mass index, skin type, and hydration levels on dermal/total skin thickness highlight the importance of a personalized approach in clinical practice. This study expands the existing literature on facial skin thickness with data from the Anatolian and Thracian populations, providing baseline reference values that may help reduce potential complications and serve as a foundation for future multicenter studies. Key words: Skin thickness, face, dermis, skin type, water intake