Parasitic copepods of the family Caligidae, otherwise known as sea lice (Lepeophtheirus salmonis and Caligus elongatus), are responsible for serious disease problems in salmon aquaculture. This mini-review examines the host factors that are affecting the susceptibility of sea lice infection in salmon; in particular, host species, environment, host stress levels, and host immunocompetency. In order to develop more effective methods to control sea lice infection, these factors should be taken into account, along with other factors such as sea lice life cycle and fecundity as well as salmon husbandry methods.