Parasitology is the study of parasitic protozoa, helminths, and arthropods, and it has traditionally been restricted to parasitic protozoa, helminths, and arthropods. Human parasitology is concerned with the morphology, life cycle, and relationship of medical parasites to their hosts and environments. Endoparasites and ectoparasites are the two types of parasites, respectively. The scope of parasitology as a biological study is determined not by the organism or environment in issue, but by their method of existence. Because of the wide range of organisms studied, the subject is frequently divided into smaller, more focused sections that employ similar approaches, even if they are not researching the same organisms or diseases. Parasites have different life cycles. Some organisms have a simple life cycle in which all developmental stages are achieved in a single host. Others necessitate the use of two distinct hosts.