What characteristic defines an acid in terms of pH?

An acid is characterized by having a pH value that is below 7.0. The pH scale ranges from 0 to 14, where values less than 7 indicate acidity, values around 7 indicate neutrality, and values above 7 represent alkalinity (basicity). Acids release hydrogen ions (H+) in solution, which is what lowers the pH. This fundamental property of acids is crucial in various applications in cosmetology, particularly in product formulations for skin care, hair care, and treatments, where maintaining the appropriate pH level is essential for effectiveness and safety. Understanding the pH scale and the characteristics of acids helps cosmetologists choose the right products for their clients and achieve desired results.