Question: why do some diseases make you die?

Ee Lyn Lim answered on 28 Jun 2013:

Diseases that cause death do it by shutting down the functions of some of your organs, and they can do it in any number of ways. If a bacteria or virus infects an important organ, it’s easy to see how – if the tuberculosis bacteria destroys your lungs, or if the Hepatitis virus stops your liver working, for example. Some bacteria are actually fairly harmless (for example if they’re just infecting a wound on your skin) but will kill you if they get into your blood – that’s because the same inflammation that makes your skin turn red and swollen around the wound will then happen in your WHOLE BODY – all your blood vessels suddenly expand let lots of water out into your tissues, so your blood pressure drops like a rock. That’s called toxic shock syndrome.

In the same way, non-infectious diseases can also kill you if they manage to shut down your organs. Heart disease is an obvious one – you can’t stay alive if your heart doesn’t pump blood! Cancer is a sneaky one, because it can destroy organs close to the tumour simply by squashing them, or it can metastasise all over the body and disable all the organs at once. Many other diseases like multiple sclerosis or muscular dystrophy also kill you by taking away your ability to move (by taking out your nerves or muscles), so that you stop being able to breathe.

Some other diseases are a bit different – they don’t kill you themselves, but they make it really easy for other diseases to kill you! HIV is a classic one. The virus attacks your immune cells – that in itself doesn’t kill you, but when other bacteria or viruses come along, you have no way of fighting back at all, and even a simple flu can kill you! Sometimes people who take immunosuppressants, such as people who have had an organ transplant, will also not have a working immune system, so diseases that are usually harmless in other people can make them extremely ill.

But, as Peter’s mentioned in another question, the only reason you die is because your brain can’t get enough oxygen! So whatever organ a disease damages, in the end it stops blood carrying enough oxygen from getting to your brain, which is when you die!