Suppression of the immune system can occur for a variety of reasons. Some people inherit conditions that affect the ability of the immune system to do its job, while others acquire problems through organ damage or infectious disease. A number of drugs can also produce suppression of the immune system, although these have their benefits in certain situations. Different stages of life can also affect the immune system's efficiency, such as old age or pregnancy, although as this is natural, it does not generally fall into the medical definition of immune suppression.
Disease is a common cause of suppression of the immune system. In healthy people, the immune system employs a variety of cells and molecules that work together to resist disease. If one or more of these normal components is affected by a medical condition, then the body is more at risk of disease. Conditions that can produce this include inherited problems like globulinemias, DiGeorge syndrome or Wiscott-Aldrich syndrome.
Some people who suffer from suppression of the immune system acquire their issues from an infection. Infectious organisms that can produce a weakened immune response include human immunodeficiency virus (HIV). Even malnutrition can result in immune suppression, as the body cannot get an adequate amount of nutrients to keep the components of the system at the necessary quality or quantity.
Organ diseases, or injury to organs, can also produce problems in the immune response, as can diabetes. Some organs, such as the spleen, are directly involved in the immune response, and their removal adversely affects the ability of the body to defend itself against infection. Certain cancers can also damage the efficiency of the immune response, or the chemotherapy treatment for the cancer patient can itself produce immune suppression.
Various drugs, including chemotherapy, have a dampening effect on the immune system. Corticosteroids, for example, are drugs that interfere with the inflammatory action of the immune system, and in reducing the immune response, indirectly reduce the ability of the immune response to defend against infection. Other drugs, like immunosuppressants for transplant patients, are used deliberately to prevent the immune system attacking the foreign material of the organ or tissue.
Very young children and pregnant women have a reduced immune strength, which can result in more infections than other people. This is normal though, as children's immune systems are not fully developed yet, and pregnant women need to prevent their immune system from attacking the unborn baby. These cases are not typically included in the definition of people suffering from immune suppression. The elderly are another group of people with a less robust response to infection, who also are not commonly included in the immune suppression group, but who need to take special care if exposed to infection.