Which of the following is NOT a service performed by a cosmetologist?

In the context of cosmetology, the practice encompasses a variety of beauty services, which typically include hair coloring, trimming eyebrows, and nail care. Performing eyelash extensions, however, falls under a more specialized category. This specific service is generally associated with estheticians or professionals specializing solely in eyelash and brow design, rather than being a core service provided by all cosmetologists.

Cosmetologists are trained in a broad spectrum of beauty services, including hair care, skin care, and nail care. Each of the other activities listed—coloring hair, trimming eyebrows, and cleansing nails—are foundational aspects of a cosmetologist's training and practice. Therefore, performing eyelash extensions is the service that does not align with the standard skill set of a typical cosmetologist, thereby making it the correct choice in identifying a service that a cosmetologist would not typically perform.