Hormones are chemicals that are made by specific cells, are released into the blood stream and travel through the body to other cells where they have a biological effect. There are many hormones made in the body. Those that are most often associated with health-related issues include thyroid hormones, insulin, parathyroid hormone, prolactin, cortisol, aldosterone, testosterone, estrogen, progesterone, epinephrine and others. Hormone-related problems may result from too much of a given hormone, too little or an abnormal pattern of hormone secretion. In addition, there are many substances that meet the definition outlined above but which are not usually thought of as hormones. For example, mediators of inflammation such as histamine or chemicals broadly labeled “cytokines” that communicate important information between immune cells are made by one cell type, released into the blood and act on other cells at distant locations. These chemicals are not labeled as hormones, but the distinction is a little bit arbitrary. The same is true of neurotransmitters–the chemicals that communicate signals between nerve cells. Epinephrine (also called adrenaline) is an example of a chemical that is sometimes thought of as a hormone–when it is made in the adrenal glands and secreted into the bloodstream–and sometimes thought of a neurotransmitter–when it is released at a nerve cell ending and travels to the adjacent nerve to communicate a signal. Obviously epinephrine is not just a hormone and not just a neurotransmitter, but both. The same is true for a number of other hormones and cytokines.