Your immune system is detecting and eliminating damaging substances, tackling bodily changes that pose a risk of illness, or simply fighting against those potentially perilous viruses and bacteria without you even being aware. Your immune system is constantly performing essential jobs. Key players in our immune systems are white blood cells. They’re produced in our bone marrow and are part of our lymphatic system. White blood cells travel through tissue and blood throughout our bodies, searching for foreign invaders (microbes) including fungi, bacteria, viruses and parasites. When our immune systems fail entirely, we're left without any natural protection against sickness. This leaves us open to “opportunistic infections” — ailments that can even come from things that normally would not harm you.

“Optimal functioning of the immune system, it turns out, is dependent upon feeling good.” - Marcey Shapiro, Freedom From Anxiety: A Holistic Approach to Emotional Well-Being