What organism lives in or on another living organism and draws nutrients without benefiting the host?

The organism that lives in or on another living organism and draws nutrients without benefiting the host is referred to as parasitic. This type of relationship is characterized by one organism, the parasite, deriving nourishment and survival from its host while potentially harming it in the process. This distinction is essential as it highlights the nature of the interaction: the parasite benefits at the expense of the host's health and well-being.

In contrast to parasitic organisms, commensal organisms may benefit from the host without harming it, while beneficial organisms contribute positively to the host's health or ecosystem. Symbiotic relationships can encompass both mutualistic interactions, where both organisms benefit, and commensal associations; therefore, the term is broader and does not specifically define the one-sided dynamic that defines parasitism. Understanding these definitions is key in fields related to biology, microbiology, and health sciences, particularly in contexts like skincare and esthetics, where knowledge of these concepts is important for practitioners.