Acidity of Base Coats and its Influence on the Structure of the Nail Plate

Against the backdrop of the rapid expansion of the global nail care segment, the issue of chemically induced damage to the nail plate associated with prolonged wear of polymer coatings is becoming particularly acute. The aim of the study is to conduct a multifactor analysis of the effects of base coat acidity on the structural and biochemical parameters of the nail plate, tracing causal links between product formulation, mechanisms of its interaction with keratin, and objectively recorded indicators of damage. The work is based on a systematic review of peer-reviewed publications from the Scopus and Web of Science databases, as well as content analysis of technical documentation and industry reports. The study demonstrates that the intact nail plate is characterized by a mildly acidic surface pH (pH ≈ 5.1), which ensures barrier properties. Acidic base coats containing methacrylic acid form adhesion through chemical etching, leading to hydrolytic cleavage of keratin peptide bonds, disruption of disulfide bridges, and a quantitatively recorded decrease in cysteine content (by 22.1%) and methionine (by 36.5%) after six months of use. These changes are accompanied by a reduction in plate thickness (from 0.50 mm to 0.46 mm) and a shift of pH into the alkaline range (to >6.0), which weakens its natural antimicrobial defenses. In contrast, acid-free systems achieve fixation through covalent bonding without compromising the integrity of the keratin matrix. The acidity of the base layer acts as a key determinant of its destructive potential. The presented data have applied value for nail technicians, cosmetic formulators, and consumers, supporting the prioritization of technologies that preserve the biochemical and structural integrity of the nail plate.