Background/Objectives: Skin color is innately determined by race and other genetic factors, and it also undergoes acquired changes due to various intrinsic and extrinsic factors. Previous studies on skin color have mainly focused on the face, and research has recently expanded to other body parts. However, there is limited information about the age-dependent changes in the skin color of these body parts. The purpose of this study is to analyze the differences in skin color between various body parts and the changes in skin color of each body part with age. Methods: This study examined the skin color of 53 Korean women subjects evenly distributed in age from the 20s to 60s on several body parts: forearm, upper arm, elbow (extended or folded), knee (extended or folded), thigh, and shin. The lightness (L*), redness (a*), and yellowness (b*) were measured using a spectrophotometer, and the individual typology angle (ITA°) was calculated from the L* and b* values. The melanin index and erythema index were measured using the mexameter. Results: The results showed that the elbow skin had the lowest L* and ITA° values and the highest a* and b* values among the examined body parts, followed by the knee. The melanin index and erythema index were also high in the skin of these body parts. In the analysis of age-dependent changes in the skin color of various body parts, the forearm skin exhibited the most notable decrease in the L* and ITA° values and increases in the a* and b* values, followed by upper-arm skin. The melanin and erythema indices in the forearm also increased as the subjects aged, whereas those in the elbow and knee rather decreased with age. Conclusions: This study suggests that differences in intrinsic and extrinsic skin aging in various body parts may be expressed as different changes in skin color and raises the need for cosmetic and dermatological research to identify the physiological significance of these changes.

The effects of orally consumed probiotics on skin wrinkles and dryness are not fully known. A randomized, placebo-controlled, triple-blinded study was conducted with 148 healthy Korean female volunteers aged between 33 and 60 years, who were administered 1.75 × 10⁹ colony-forming units (CFUs) of Bifidobacterium animalis subsp. lactis Bl-04 (Bl-04) (N = 74) or matching placebo (N = 74) for 12 weeks. Facial wrinkles (with 3-dimensional (3D) imaging), skin hydration, transepidermal water loss (TEWL), elasticity, and gloss were assessed at baseline and after every 4 weeks of the intervention. Questionnaire-based subjective evaluations of product efficacy and usability were also analyzed. The consumption of Bl-04 was safe and ameliorated significantly facial skin wrinkle parameters (total wrinkle area and volume, average depth of wrinkles, and arithmetic average roughness (Ra)) versus placebo at 4 weeks, but there were no differences at Week 8 or 12 between groups. Skin hydration, TEWL, elasticity, and gloss were similar between treatment groups, as were the subjective evaluation scores. Oral consumption of Bl-04 indicated promising short-term effects on skin appearance from the winter toward the spring. In future study designs, special attention should be paid to environmental conditions as well as to the skin condition and age of the participants.

Background/Objectives: Ultraviolet radiation (UVR) induces oxidative stress in the skin by generating reactive oxygen species (ROS), which can lead to inflammatory conditions including erythema (a sign of sunburn). This clinical study aims to develop an instrumental evaluation method to determine the minimal erythema dose (MED) for UVR. Methods: Fourteen human subjects aged 27 to 57 years (48.93 ± 8.54) participated in this study. Six subsites were designated on the test skin site of each subject and irradiated with UVR at different doses. The examiner visually assessed erythema, determining the ‘visual MED’. Additionally, the a* value (a chrominance parameter presenting greenness to redness) was measured using a spectrophotometer as an indicator of erythema. The a* values of the UVR-irradiated subsites were compared to the non-irradiated control value, and the differences were referred to as Δa*. The Δa* value of the subsites irradiated with UVR at the ‘visual MED’ was referred to as the Δa*_VMED for each subject. The mean of the Δa*_VMED values of all subjects was chosen as a criterion value for the ‘instrumental MED’. The ‘instrumental MED’ was defined as the lowest dose of UVR that causes an Δa* value equivalent to the criterion value. The ‘visual MED’ and ‘instrumental MED’ values of all subjects were subjected to correlation analysis. Results: The mean of the Δa*_VMED values of all subjects was 1.88 ± 0.8. The means of the ‘visual MED’ and ‘instrumental MED’ values (in J m⁻² unit) of all subjects were 300.14 ± 84.16 and 303.29 ± 77.99, respectively. In Pearson correlation analysis, the ‘instrumental MED’ and ‘visual MED’ values had a very strong positive correlation with each other (r = 0.864, p = 0.000). Conclusions: This study suggests that the instrumental evaluation method of MED based on the spectrophotometric measurement of the a* values can complement or replace the visual evaluation method and that this method will be useful in monitoring skin tolerance to oxidative stress affected by prooxidant factors and defensive factors.

Skin aging is characterized by decreased collagen synthesis and increased extracellular matrix degradation, leading to wrinkle formation and reduced skin elasticity. This study evaluated the anti-aging potential of hydrolyzed fish skin (HFS) extract through complementary in vitro and clinical investigations. In human dermal fibroblasts, treatment with HFS extract enhanced type I procollagen production and suppressed UVB-induced matrix-degrading enzymes, including matrix metalloproteinase-1 (MMP-1) and elastase, suggesting a mechanism that supports dermal matrix homeostasis. A randomized, double-blind, split-face clinical trial was conducted in 20 female participants over 12 weeks. A formulation containing 0.5% HFS extract was applied to one side of the face, while an identical vehicle control formulation without HFS extract was applied to the contralateral side. Wrinkle parameters were assessed using a three-dimensional imaging system. After 12 weeks, the test group showed significant improvements compared to baseline, with reductions of 12.75% in arithmetic mean roughness (Ra), 12.46% in root mean square roughness (Rq), and 11.32% in maximum wrinkle height (Rmax) (p < 0.05). No adverse events were observed. These findings demonstrate that HFS extract improves wrinkle-related skin parameters, potentially through promoting collagen synthesis while inhibiting matrix degradation. The combined molecular and clinical evidence supports its application as a functional cosmetic ingredient in anti-aging formulations.

Skin changes in women around age 40 are often attributed to impaired barrier function or reduced hydration, but large-scale data comparing sebum, hydration, and transepidermal water loss (TEWL) across age groups are scarce. In this cross-sectional study, we analyzed standardized cheek measurements from 7743 women aged 20–59 years in 12 countries (5274 Asian and 2469 Western). Piecewise regression tested changes in age-related slopes at age 40, including differences by region. The negative age–sebum slope was significantly steeper from age 40 onward in both Western (slope change −0.762 µg/cm²/year, p = 0.010) and Asian women (−1.256 µg/cm²/year, p < 0.001), a result that held with robust standard errors, log transformation, and country adjustment and was replicated at two other facial sites. Hydration showed no change in slope at age 40, and resting TEWL decreased rather than increased. Sebum was 34.9% (Asian) and 25.4% (Western) lower at 50–59 than at 20–29 years, whereas hydration differed by less than 3.5%. Men showed a different pattern, with no net sebum difference between these age groups. The regional difference in slope change was not significant (p = 0.168). After age 40, the oil–moisture profile of women is characterized by lower sebum with stable hydration; longitudinal studies with hormonal assessment should test whether this reflects menopause.

Skin hydration is not uniform: it is low at the surface and rises with depth, and the standard capacitance probe (Corneometer) samples only the outermost layer. How the surface–deep relationship evolves under repeated moisturizer use is not captured by a single metric. Using the Hydration Gap Index (HGI = |surface − deep (0.5 mm)|), this relationship was tracked in 22 healthy adults, measuring surface hydration (Corneometer) and depth-resolved deep hydration (Moisturemeter D; 0.5–5.0 mm) at baseline, after one application, and after two weeks. Surface hydration rose sharply after one application (30.9 → 64.0 A.U.), then partially declined by two weeks (43.5 A.U.; all p < 0.001), whereas deeper readings were essentially unchanged (≤5.1%), consistent with a stable deep compartment. The per-subject surface–deep gap first widened (13.1 → 18.0) then narrowed to ≈5.1 A.U. (19/22 subjects; group-mean 2.0). Surface and deep compartments varied independently (baseline r = −0.14; change r = +0.05), and the surface-dominant response was reproduced with a different surface instrument in the same cohort (surface +102%, deep +4%). The apparent depth gradient steepened only through this shallow-layer gain (−3.66 → −3.93 A.U./mm, p < 0.0001). Thus, repeated use reflected equilibration of the superficial layer toward the 0.5 mm compartment, not a uniform rise; the HGI provides a compact index of this surface-to-deep equilibration.