Host factor (sometimes known as risk factor)[1] is a medical term referring to the traits of an individual person or animal that affect susceptibility to disease, especially in comparison to other individuals.[2] The term arose in the context of infectious disease research, in contrast to "organism factors", such as the virulence and infectivity of a microbe. Host factors that may vary in a population and affect disease susceptibility can be innate or acquired.
Some examples:
The term is now used in oncology and many other medical contexts related to individual differences of disease vulnerability.