Outside and Inside …or, using medical terminology, exogenous and endogenous (exô = Greek, outside; endô = Greek, inside; gçno = origin/beginning: 'originating from outside/inside'). If treatments of signs and symptoms concentrate exclusively on occurrences within the system, many factors outside the affected individual are ignored. Research throughout the world is showing that we, as humans, are influenced both by what is outside and by what is inside. People are becoming more susceptible to outside – exogenous – factors, such as diet and environment. If we consider immunity – a synonym of immunity is exemption – we can understand that the body may be exempt from symptoms (and usually signs) after an outside challenge. But how does this exemption arise? Barriers, that's how. Inside barriers include white blood cells called macrophages, which engulf 'foreign' items (e.g. bacteria). These macrophages, together with other cells such as B- and T-lymphocytes, contain enzymes that break down the foreign items. The human immune system uses a vast network of 'test–react–retest–modify–remember' reactions, when challenged by outside agents. The immune system is present anywhere there may be a challenge: mouth, lungs, skin, bowel, to name but a very few. That is, you will find the immune system everywhere! Lymph nodes are collection points along the lymph ducts where the various immune cells gather. These are the 'swollen glands' you can feel in your throat when you have a throat infection. Comparing exogenous (outside) stimuli with endogenous (inside) stimuli, sometimes a person's immune system is mistaken: the 'self' is incorrectly identified as 'foreign' and recent research has shown that some skin and bowel conditions are as a result of mistaken identity by the body's own immune system.