Photosafety assessments are a key requirement for the safe development of pharmaceuticals, cosmetics, and agrochemicals. Although in vitro methods are widely used for phototoxicity and photoallergy testing, their limited applicability and predictive power often necessitate supplemental in vivo studies. To address this, we developed the PhotoChem Reference Chemical Database, comprising 251 reference compounds with curated data from in vitro, in vivo, and human studies. Using this database, we evaluated the predictive capacity of three OECD in vitro test guidelines—TG 432 (3T3 NRU), TG 495 (ROS assay), and TG 498 (reconstructed human epidermis)—by comparing the results against human and animal data. Against human reference data, all three test methods showed high sensitivity (≥82.6%) and strong overall accuracy: TG 432 (accuracy: 94.2% (49/52)), TG 495 (100% (27/27)), and TG 498 (86.7% (26/30)). In comparison with animal data, sensitivity remained high for all tests (≥92.0%), while specificity varied: TG 432 (54.3% (19/35)), TG 495 (63.6% (7/11)), and TG 498 (90.5% (19/21)). TG 498 demonstrated the most balanced performance in both sensitivity and specificity across datasets. We also analyzed 106 drug approvals from major regulatory agencies to assess real-world application of photosafety testing. Since the mid-2000s, the use of in vitro phototoxicity assays has steadily increased in Korea, particularly following the 2021 revision of the MFDS regulations. Test method preferences varied by region, with 3T3 NRU and ROS assays most widely used to evaluate phototoxicity, while photo-LLNA and guinea pig tests were frequently employed for photoallergy assay. Collectively, this study provides a valuable reference for optimizing test method selection and supports the broader adoption of validated, human-relevant non-animal photosafety assessment strategies.

Calcium nitrate tetrahydrate, used in fertilizers, wastewater treatment, and concrete admixtures, has limited toxicity data despite extensive industrial use. This study evaluated its repeated-dose and reproductive/developmental toxicity in Sprague Dawley rats following OECD TG 422, which combines TG 407 and 421 to extend dosing than TG 407 and reduce animal use compared with separate studies. Rats were administered 0, 100, 300, or 1000 mg/kg/day. Males were treated for 49 days and females from 2 weeks pre-mating to postpartum day 13; the recovery group was observed for an additional 2 weeks. Endpoints included clinical signs, body weight, food consumption, hematology, serum biochemistry, organ weights, histopathology, reproductive performance, and F1 development. No systemic toxicity was observed in F0 males. Minimal prostate atrophy occurred in high-dose males but was considered non-adverse due to limited severity. One high-dose female died on PPD 1, and high-dose F1 litters showed decreased litter size, increased post-implantation loss, and a reduced live-born index. Based on these results, NOAELs were cautiously assigned 1000 mg/kg/day for repeated-dose and male reproductive toxicity and 300 mg/kg/day for female reproductive and developmental toxicity. TG 422 efficiently characterized hazards while reducing animal use, though its limited duration and scope indicate the need for complementary studies.

Moisturizers are key components of skincare products, and reliable test methods are essential for evaluating their barrier-repairing and hydrating efficacy. However, the viscous and waxy nature of many cosmetic moisturizers limits the applicability of conventional cell-based in vitro assays. In this study, we developed a novel in vitro dry skin model using epidermal sheets from minipig and human cadaver skin—models widely accepted in skin absorption research. To simulate dry skin conditions, various stimuli were applied, including the lipid-extracting solvent tert-butyl methyl ether (MTBE; 100%), 50/50 MTBE/Acetone solution (M/A), the irritant surfactant sodium dodecyl sulfate (SDS; 1%), ultraviolet B (UVB) irradiation (30 mJ/cm²), and tape stripping. Skin barrier disruption and stratum corneum damage were evaluated by assessing epidermal lipid integrity, histological alterations, transepidermal water loss (TEWL), and FITC-dextran permeation. All treatments induced significant dry skin conditions, as evidenced by disrupted lipid architecture, histological damage, and increased TEWL and FITC-dextran flux. Among them, M/A applied for 5 min produced the most consistent and reproducible changes across parameters. This protocol also yielded comparable results in human cadaver skin, supporting its applicability for evaluating the skin barrier-protective effects of cosmetic ingredients.