Alpha-hydroxy acids (AHAs), such as glycolic acid, are commonly used in cosmetics and dermatology, particularly for their exfoliating properties. In concentrations of 2-5%, glycolic acid is thought to weaken the bonding between cells in the outer layer of the skin (stratum corneum or SC), leading to a gradual shedding of the top skin layers. While this exfoliation can improve skin texture, concerns have been raised about whether it might harm the skin’s barrier function and increase water loss through the skin (transepidermal water loss or TEWL).To explore this, a study was conducted on human volunteers who used a 4% glycolic acid formulation twice a day for 3 weeks. The goal was to examine how glycolic acid affected the structure and function of the SC. The researchers used electron microscopy to analyze skin samples taken from the forearm, focusing on the overall skin structure and thickness of the SC, the organization of lipids and lamellar bodies (which help with skin barrier function), and changes in desmosomes (structures that hold skin cells together).