Question: Why does the body sometimes attack itself? because apart from getting other damage like neurodegenerative damage you could get cancer from it. Why would the body want to damage itself in the first place?

Max Jamilly answered on 15 Mar 2018:

Great question! The body never *wants* to damage itself, but sometimes, like all good machines, it just goes wrong.
Every cell in the body has special signals on its surface to indicate that it’s a ‘friendly’ cell. When an immune cell comes along to check, they exchange a secret handshake and the immune cell knows that the other cell isn’t a threat. On the other hand, foreign cells (from invading microbes, or some cancer cells which have lost control) don’t have these signals so they can’t do the secret handshake. Immune cells detect these unwanted cells and attack them.
This goes wrong when cells stop displaying the right signals or the immune system forgets how to do the secret handshake. As a result, the immune system thinks that friendly cells are invaders and starts to attack them. This is what we call autoimmune disease. It can happen due to genetics, viral infections or as a side effect of some medicines. We’re working hard to understand more about what causes it and how to prevent it!