The immune system is a network of cells that join together to combat the body against the attacks of a foreign invaders. These foreign invaders are mainly microbes such as parasites, fungi, and bacteria. Viruses are also considered foreign invaders to the body. The immune system’s job is to keep these foreign invaders out of the body. If some of them do come in the body, then it’s job is to kill them. A pathogen can be viewed as an infectious agent. It causes illness or disease to its host. It causes chaos in the normal physiology of a multi-cellular plant or animal. It can also infect unicellular organisms as well. One of the immune system’s most important functions is the ability to distinguish between the body’s own cells as “self” and foreign cells as “non self.” The immune system usually works together quietly with cells that are classified as “self” cells. When an immune system detects a foreign organism or cell categorized as “non self,” it quickly fires an attack. In abnormal circumstances, the immune system can order an attack by mistake on its own cells. This is known as autoimmune disease. There are many types of nonspecific defenses that the immune system uses. The three types of nonspecific defenses I am going to talk about are traps, barriers, and low level of pH. Some of the examples of traps are hair, cilia, ear wax, and mucous membranes. Mucous membrane and skin are the first line of defense, also called along innate immunity, in a person’s body. Mucous membrane borders the respiratory, GI, and genitourinary tract. The mucous membrane produces sticky glycoprotein fluid called mucus. Cilia, tiny hair-like projections, move the mucus up to the esophagus where it can be swallowed by a person. Mucus operates as a mechanical shield to microbes and prevents the tracts from condensing. Skin is the largest organ in the body so it provides the