Immune System

As people age, the immune system becomes less effective. But the change is so slight that most people do not notice it. Most people notice that the body is less able to fight infections only when infections linger or become severe. People who are infected with tuberculosis during early adulthood may have no symptoms until old age. Then, symptoms develop because the immune system is weaker.

The immune system may be less able to distinguish the body's own cells from foreign substances that invade the body. Consequently, disorders in which the immune system attacks some of the body's own cells (autoimmune disorders) become more common.

The cells of the immune system destroy cancer cells, bacteria, and other foreign substances more slowly. This slowdown may be one reason that cancer is more common among older people. Also, vaccines tend to be less protective in older people. These changes in the immune system may help explain why some infections, such as pneumonia and influenza, are more common among older people and result in death more often.

Changes in the immune system may have one beneficial effect. Allergy symptoms may become less severe.