As people age, the immune system begins a process of restructuring and immune organs begin to slow, reducing their ability to fully function as they go through physiological involution. Innate immunity is a non-specific system including physical barriers such as skin, stomach acid, and mucosal membranes.

The result is an overall reduced ability for immune cells to recognize antigenic variation, diminishing the ability of the immune system to recognize and fight pathogens. Aging in the immune system also corresponds with an increased secretion of cytokines (the immune system’s chemical messengers) and a reduction in macrophages and natural killer cells. (Macrophages are white blood cells that kill invading pathogenic microorganisms, remove dead cells, stimulate immunity and tissue repair, and produce inflammatory and antimicrobial compounds.)