A person who is undergoing immunosuppression, or whose immune system is weak for some other reasons (such as chemotherapy or HIV), is said to be immunocompromised.

[7] Dr. Joseph Murray of Brigham and Women's Hospital was given the Nobel Prize in Physiology or Medicine in 1990 for work on immunosuppression.

[8] Immunosuppressive drugs have the potential to cause immunodeficiency, which can increase susceptibility to opportunistic infection and decrease cancer immunosurveillance.

[11][12][13] Non-deliberate immunosuppression can occur in, for example, ataxia–telangiectasia, complement deficiencies, many types of cancer, and certain chronic infections such as human immunodeficiency virus (HIV).

The unwanted effect in non-deliberate immunosuppression is immunodeficiency that results in increased susceptibility to pathogens, such as bacteria and viruses.