Our immune systems can save us, maim us, or kill us. Very few understand it and most neglect it.
From the beginning of life through death, our immune system is playing a critical role every single day in preventing or limiting infection. It does it by determining the difference between normal, healthy cells and unhealthy cells. Unhealthy cells can be compromised by infectious agents or damaged by injuries or even cancer. The immune system also recognizes viruses and bacteria by the signals they put out.
When alerted the immune system responds to the problem. If an immune response is not activated by a need, problems arise such as infections. And then there are times when an immune response is activated without a real threat or is not turned off once a danger has passed. Allergic reactions and autoimmune diseases are symptoms of that event.
Understanding your immune system is critically important if you want to strengthen it and keep it from running amuck.