The brain and the immune system are in constant communication, in a delicate balance that can be thrown off by chronic stress. The hypothalamus plays a key role in the stress response, releasing corticotropin-releasing hormone (CRH). CRH stimulates the pituitary gland beneath the hypothalamus to release another hormone, adrenocorticotropin hormone (ACTH), into the bloodstream. ACTH then causes the adrenal glands — located above the kidneys — to release the stress hormone cortisol. In addition to alerting the body to meet stressful situations, cortisol helps regulate the immune system. The hypothalamus uses both cortisol and signal molecules from the immune system called cytokines to monitor the situation in the body and ensure that there isn’t an immune system overreaction that harms healthy cells and tissues. Problems anywhere in this complicated communications system, whether caused either by extreme stress or by faulty genetics, can lead to disease.