How the Immune System Works (and Why "Boosting" Is Oversimplified)

What the immune system is

The immune system is a network of cells, tissues and organs that helps the body fight infections and other diseases. [1] It includes the skin, the moist linings called mucous membranes, white blood cells, and parts of the lymph system such as the thymus, spleen, tonsils, lymph nodes and bone marrow. [1]

Innate immunity: the first line of defense

Innate immunity is the protection you are born with. It includes barriers such as the skin and mucous membranes, plus some cells and chemicals that can attack foreign substances. [1] MedlinePlus lists the cough reflex and enzymes in tears and skin oils as examples. [2]

Adaptive immunity: learning and remembering

Adaptive (also called active) immunity develops when you are infected with, or vaccinated against, a foreign substance, and it is usually long-lasting. [1] When the immune system recognizes an antigen (a substance it sees as foreign), it attacks it and makes antibodies, which are proteins that attack, weaken and destroy antigens. Afterward it remembers the antigen and can respond quickly if it appears again. [1]

A third type, passive immunity, happens when you receive antibodies instead of making them, for example newborns receive antibodies from their mothers. It protects right away but only for weeks or months. [1]

Inflammation: a normal part of defense

Inflammation occurs when tissues are injured by bacteria, trauma, toxins, heat or other causes. Damaged cells release chemicals that make blood vessels leak fluid, which causes swelling and helps isolate the foreign substance. White blood cells called phagocytes are drawn in to clear germs and damaged cells. [2] So inflammation is not simply "bad": it is part of how the body responds. Problems arise when it is out of proportion or does not switch off. Pages on specific conditions cover that; this page does not suggest any food or supplement "reduces inflammation".

How vaccines use this system

Vaccines contain only killed or weakened forms of germs, so they do not cause the disease. They train the immune system to create antibodies, as it does when exposed to the disease. [3] See vaccines and infection prevention.

When the immune system goes wrong

MedlinePlus describes three broad patterns:

See allergies vs colds and immunodeficiency, autoimmune conditions and immunosuppression.

Why "immune boosting" is oversimplified

Because the immune system can misfire in both directions, "more activity" is not automatically better. In autoimmune diseases the immune system attacks healthy cells by mistake. [4] A product marketed to "boost" immunity does not tell you which part of this network it affects, in whom, or whether that leads to fewer infections. Immune health products make up roughly 10% of US dietary supplement sales, and a systematic review of 39 randomized studies of ingredients like echinacea, elderberry, garlic, vitamins and zinc could not make firm statements about the overall evidence. [5] Laboratory markers (such as cell counts) are also not the same as fewer infections, so look for outcomes like number of colds or days of illness. See supporting immune health and research and evidence.