Qualitative indicators are an important element in establishing truth in polygraph examinations. Considering this, a study of the change in the quality of the signal from the photoplethysmograph in subjects who have used nail polish is extremely relevant and requires a comprehensive qualitative study. Th e paper uses general scientifi c and empirical methods of observation and experimentation, and is a comprehensive study of the eff ects of nail polish on the quality of the photoplethysmograph signal. It is the fi rst time that this type of research has been conducted using a comparative analysis of subjects who did and did not use nail polish.