En español

A person’s immune system may not function efficiently for a variety of reasons. In some cases, the situation is brief. In other cases, the compromised immune response can be lifelong. Some reasons for immune deficiencies include genetic disorders and use of medications. Another reason is current, or ongoing, infections. 

Another situation that can affect the efficiency of the immune system is autoimmunity. This occurs when the immune system mounts a response against some part of that person’s own body. Most of the time, the immune system can distinguish between what is foreign and what is not. This is called tolerance. When the immune system does not distinguish between foreign and not, people may develop diseases that result when part of the body is attacked. Type 1 diabetes is an example. In type 1 diabetes, the cells in the pancreas that produce insulin are attacked. Autoimmunity also plays a role in some medical treatments that involve using donations from one individual to treat another. An example is organ transplants. 

The immune system can also mount unnecessary responses on occasion that lead to allergic reactions. Very rarely, the immune system can mount a vigorous response to infection that causes the body to be overwhelmed. This response is sometimes called a “cytokine storm," which can be fatal.

Find out more about how the immune system can malfunction.

Reviewed by Paul A. Offit, MD, on Nov. 20, 2025