Autoimmune diseases are caused by an overactive immune system which incorporates different parts of the body – including certain blood cells, skin, bone marrow and more – that work to keep you healthy. Our immune system protects us from infection by detecting and fighting diseases. If infectious agents such as bacteria or viruses get into your body, immune cells usually kill or overwhelm them, removing the infection. This is known as the immune response.
Autoimmune disease occurs when, instead of attacking bacteria, viruses or other sources of infection, the immune system attacks healthy organs and tissues. It’s not known why this happens, although autoimmune conditions most often affect people with a genetic predisposition. An environmental factor such as an infection, stress, medication, diet or even ultraviolet radiation then triggers the symptoms of the autoimmune disease. Micro-organisms that live in the gut might also influence autoimmune responses. While this explains why autoimmune disease occurs generally, it’s not usually possible for us as clinicians to determine why it occurs in one particular individual.