Immune disorders occur when the body’s natural immune system is unable to differentiate between harmful and healthy bacteria or antigens in the body, leading the immune system to mistakenly attack the antigens of healthy body tissues rather than of harmful bacteria, toxins, viruses, and other cells that may enter or grow in the body. Having an untreated immune disorder can lead to harmful changes in normal organ function, including abnormal growth of an organ, and unnecessary destruction of healthy tissues. It is possible to have more than one immune disorder at once, and they can affect just about anywhere in the body but most frequently attack the connective tissues, the joints, muscles, skin, the pancreas, blood vessels, and red blood cells.