What are parasites?

Parasites are defined as pathogenic organisms that require a host to survive and reproduce. This means they depend on another organism, often causing harm or disease to that host in the process. Parasites can include a variety of organisms such as protozoa, worms, and ectoparasites like lice and mites. Understanding this definition is crucial in fields like skin science and dermatology, as certain parasites can lead to significant skin conditions or infections.

The other options do not accurately capture the definition or characteristics of parasites. Non-infectious skin disorders refer to skin issues that are not caused by pathogens, which is distinctly different from the nature of parasites. Healthy bacteria, on the other hand, typically contribute to skin health and are classified as beneficial microbiota, not parasites. Lastly, while direct infections that affect blood cells can occur in the presence of certain pathogens, they do not specifically describe parasites, which operate in a different manner involving a host organism.