Immune system aging is a growing public health concern due to increased life expectancy and reduced health expectancy. As people age, both innate and adaptive immune systems undergo changes, known as inflammaging and immunosenescence, leading to increased vulnerability to infections and reduced vaccine effectiveness. This review discusses the changes in the aging immune system and their impact on age-related infectious diseases. Aging is a complex process involving multiple biological, social, and psychological factors. It is characterized by a progressive loss of function, including genomic instability, telomere shortening, and chronic inflammation. These changes are closely linked, contributing to a state of immunodeficiency and increased susceptibility to infections. Inflammaging is a chronic, low-grade inflammation associated with aging, characterized by increased pro-inflammatory cytokines and decreased anti-inflammatory cytokines. Senescent immune cells produce a "senescence-associated secretory phenotype" (SASP), contributing to chronic inflammation. Age-related immune changes include reduced numbers of immune cells, impaired function of neutrophils and macrophages, and altered T and B cell responses. These changes are influenced by factors such as lifestyle, diet, and environmental exposure. Sex differences also play a role in immune aging, with older men showing higher monocyte activity and older women having a slower decline in immune function. The immune system becomes more complex with age, with changes in cell composition, function, and interactions. Biomarkers such as IL-6, TNF-α, and telomere length are used to assess immune aging. The study of age-related immune variations has advanced with the use of system immunology, allowing for a better understanding of immune function at the population and single-cell levels. In infectious diseases, immune aging contributes to increased susceptibility, severity, and outcomes. Viral infections such as HIV, influenza, and VZV are associated with immune aging, leading to increased inflammation and reduced immune function. Bacterial infections such as tuberculosis are also influenced by immune aging, with older adults being more susceptible to recurrent infections. Understanding these changes is essential for developing strategies to promote healthy aging and improve immune function in older adults.Immune system aging is a growing public health concern due to increased life expectancy and reduced health expectancy. As people age, both innate and adaptive immune systems undergo changes, known as inflammaging and immunosenescence, leading to increased vulnerability to infections and reduced vaccine effectiveness. This review discusses the changes in the aging immune system and their impact on age-related infectious diseases. Aging is a complex process involving multiple biological, social, and psychological factors. It is characterized by a progressive loss of function, including genomic instability, telomere shortening, and chronic inflammation. These changes are closely linked, contributing to a state of immunodeficiency and increased susceptibility to infections. Inflammaging is a chronic, low-grade inflammation associated with aging, characterized by increased pro-inflammatory cytokines and decreased anti-inflammatory cytokines. Senescent immune cells produce a "senescence-associated secretory phenotype" (SASP), contributing to chronic inflammation. Age-related immune changes include reduced numbers of immune cells, impaired function of neutrophils and macrophages, and altered T and B cell responses. These changes are influenced by factors such as lifestyle, diet, and environmental exposure. Sex differences also play a role in immune aging, with older men showing higher monocyte activity and older women having a slower decline in immune function. The immune system becomes more complex with age, with changes in cell composition, function, and interactions. Biomarkers such as IL-6, TNF-α, and telomere length are used to assess immune aging. The study of age-related immune variations has advanced with the use of system immunology, allowing for a better understanding of immune function at the population and single-cell levels. In infectious diseases, immune aging contributes to increased susceptibility, severity, and outcomes. Viral infections such as HIV, influenza, and VZV are associated with immune aging, leading to increased inflammation and reduced immune function. Bacterial infections such as tuberculosis are also influenced by immune aging, with older adults being more susceptible to recurrent infections. Understanding these changes is essential for developing strategies to promote healthy aging and improve immune function in older adults.