Homeopathic consultant well versed with Weak immune system Weak immune system refers to an underactive and poor performing immune system. The immune system’s prime function is to protect the body against infection and the development of cancer. Support and enhancement of the immune system is perhaps the most important step in achieving resistance to disease and reducing susceptibility to colds, flus, and cancer. Supporting the immune system involves a health-promoting lifestyle, stress management, exercise, diet, and the appropriate use of nutritional supplements and herbal medicines.