Since the European Union (EU) announced their animal testing ban in 2013, all animal experiments related to cosmetics have been prohibited, creating a demand for alternatives to animal experiments for skin studies. Here, we investigated whether an ex vivo live porcine skin model can be employed to study the safety and skin barrier-improving effects of hydroxyacids widely used in cosmetics for keratolytic peels. Glycolic acid (1–10%), salicylic acid (0.2–2%), and lactobionic acid (1.2–12%) were used as representative substances for α-hydroxyacid (AHA), β-hydroxyacid (BHA), and polyhydroxyacid (PHA), respectively. When hydroxyacids were applied at high concentrations on the porcine skin every other day for 6 days, tissue viability was reduced to 50–80%, suggesting that the toxicity of cosmetic ingredients can be evaluated with this model. Based on tissue viability, the treatment scheme was changed to a single exposure for 20 min. The protective effects of a single exposure of hydroxyacids on skin barrier function were evaluated by examining rhodamine permeability and epidermal structural components of barrier function using immunohistochemistry (IHC) and immunofluorescence (IF) staining. Lactobionic acid (PHAs) improved skin barrier function most compared to other AHAs and BHAs. Most importantly, trans-epidermal water loss (TEWL), an important functional marker of skin barrier function, could be measured with this model, which confirmed the significant skin barrier-protective effects of PHAs. Collectively, we demonstrated that the ex vivo live full-thickness porcine skin model can be an excellent alternative to animal experiments for skin studies on the safety and efficacy of cosmetic ingredients.

Cleaners such as dishwashing liquids contain various chemicals that cause skin damage. Alkaline agents used in cleaners alter the lipid composition of the skin and damage the skin barrier. However, little is known about the effects of acids used in cleaners on the skin. Here, we investigated the effects of acidic pH on the skin and evaluated the skin irritation of acids commonly used in cleaners with a 3D-reconstructed human epidermis model, KeraSkin^TM, according to OECD TG439. First, to examine the effects of acidic pH, we evaluated the skin irritation of citrate buffers (0.1 M, McIlvaine buffer) prepared in a wide pH range (pH 1.5–6.0). Surprisingly, cell viability was not significantly affected even at pH 1.5, reflecting that the acidity alone may not be sufficient to induce skin irritation. Even after longer exposure (180 min), the cell viability was not reduced below 50%, a cutoff to determine an irritant. To examine the effect of the anionic part, several organic acids used in cleaners (citric acid, glycolic acid, lactic acid, malic acid, and succinic acid) were examined. These organic acids also failed to reduce viability at 0.1 M. However, at 1 M, most of the acids tested, except lactic acid, were determined to be skin irritants. Histology further supported the skin irritancy of acids at 1 M. Similarly, inorganic acids (hydrogen bromide, hydrogen chloride, nitric acid, and sulfuric acid) were determined to be irritants only at 1 M. In the case of alkaline agents, pH and concentrations were also important factors to determine the skin irritancy, although the epidermal structure and lipids were more damaged than acids. Collectively, we demonstrated that both the pH and concentration are important factors for the skin irritancy of acids, shedding an important insight into the mechanism of skin irritation.

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.