A portal of entry is the site through which micro-organisms enter the susceptible host and cause disease/infection. Infectious agents enter the body through various portals, including the mucous membranes, the skin, the respiratory and the gastrointestinal tracts. Pathogens often enter the body of the host through the same route they exited the reservoir; for example, airborne pathogens from one personís sneeze can enter through the nose of another person.
The skin normally serves as a barrier to infection. However, any break in the skin invites the entrance of pathogens, such as tubes placed in body cavities (catheters) or punctures produced by invasive procedures (needles, IV).