The GB/T 13531.1-2008 standard specifies the determination method of the pH value of cosmetics. The standard is applicable to all kinds of cosmetics and aims to determine the pH value of products through standardized testing procedures to ensure that it meets the requirements of safety and effect in use. The standard describes in detail the measurement procedures, required instruments, operating conditions and data processing methods to ensure the accuracy and conformity of the measurement results. The method provides a scientific basis for the quality control of cosmetics and helps to maintain the safety of consumers and the effectiveness of products.