Before starting a manicure, which of the following is a critical step?

Sanitizing hands is a critical step before starting a manicure because it ensures the safety and hygiene of both the client and the manicurist. Proper sanitation helps prevent the spread of bacteria, fungi, and viruses that could lead to infections or other health issues. By sanitizing hands, the manicurist creates a clean environment, upholding professional standards and promoting overall client trust and comfort.

While engaging in small talk can enhance the client's experience and choosing colors is important for aesthetics, these steps do not directly impact health and safety in the same way that sanitizing does. Checking the nail shape is more of a preparatory step in the process but does not address the essential hygiene concerns that sanitizing hands accomplishes. Therefore, sanitizing hands stands out as the fundamental step to prioritize before beginning any manicure service.