At birth, humans have very little immunity against germs and diseases. This is why newborns aren’t immediately exposed to the outside world. Nevertheless, the immune system is an intricate and highly effective mechanism designed to defend your body against health threats, often reacting within a short period of time.

Understanding the immune system has evolved over centuries. Even today, many details remain unknown. The earliest theories date back to Hippocrates, who suggested that health depended on a balance of four bodily fluids: phlegm, blood, black bile, and yellow bile. Modern science has revealed a far more sophisticated reality behind immunity…