Harmonizing In Vitro Techniques for Anti-Aging Cosmetic Ingredient Assessment: A Comprehensive Review

Skin grows old due to intrinsic factors, such as age and associated hormonal changes, and external factors, like solar radiation and chemical substances to which we are exposed. With age, skin shows thinning, laxity, pallor, increased dryness, and the appearance of wrinkles, attributed to a decrease in collagen and elastin produced by fibroblasts. Several theories explain skin aging, including the free radical formation, neuroendocrine, and mitochondrial decline theories. Based on a scientific understanding of skin behavior, different in vitro methods are used to evaluate the effects of new ingredients in cosmetics. Commonly used methods include anti-collagenase, anti-elastase, and anti-hyaluronidase activity alongside techniques utilizing skin cells or 3D models. Although these methods are recognized and widely used, they lack standardization. In this review, a literature search has been conducted to examine the characteristics and variations of these methods across the laboratories. A key issue identified in this review is that many papers provide insufficient detail regarding their protocols. Moreover, the number of studies using cells is less significant than the ones determining enzyme inhibition. Our findings revealed that, in many cases, there is limited information available, underscoring the urgent need to initiate a comprehensive standardization process for the methodologies used to demonstrate anti-aging activity.