Which of the following is considered an act of unprofessional behavior by an esthetician?

Using inappropriate language with clients is indeed considered an act of unprofessional behavior by an esthetician because it undermines the trust and comfort essential to the client-esthetician relationship. Professionalism in esthetics involves not only technical skills and knowledge but also effective communication and respecting the client’s preferences and boundaries. Using language that is unprofessional can create a negative environment and may discourage clients from returning or referring others.

In terms of the other choices, providing skin care under hygienic conditions aligns with professional standards and regulatory requirements aimed at ensuring client safety and wellbeing. Offering complimentary treatments, while it needs to be done within the bounds of ethical practices, can also be seen as a marketing strategy and a way to build client relationships. Maintaining a professional appearance is part of the industry standard for estheticians, as it reflects the professionalism and quality of the services provided. Each of these alternative behaviors supports a positive, professional atmosphere, in contrast to the negative implications of using inappropriate language.