Something living in you, or something going wrong
Why Do You Get Ill?
Illness comes in two very different kinds, and telling them apart is the first thing anyone treating you needs to know.
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Step 1 of 5
Some illnesses are living things.
Bacteria and viruses get inside, multiply using your body as food and shelter, and the damage they do is what you feel. These are the ones that spread.
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Step 2 of 5
Symptoms are often your own defence.
A fever, a runny nose and a cough are your body fighting rather than the germ attacking. Heat slows microbes down and mucus carries them out.
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Step 3 of 5
Other illnesses are not caught at all.
Something built into you can wear out, run short or be made wrongly. Nobody catches short sight or a broken bone, and no amount of hand-washing prevents them.
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Step 4 of 5
Which kind it is decides the treatment.
A microbe can be killed or waited out. A body that is short of something has to be given it, and a body that is doing too much has to be calmed down.
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Step 5 of 5
Most infections end without treatment.
Your immune system learns the shape of an invader and clears it. That is why a cold ends in a week whether or not anything was taken for it.
Being able to say which kind an illness is took centuries. Before germs were known, infections and everything else were treated as the same thing, mostly badly.
The short version
Illness is either something living multiplying inside you or the body's own workings going wrong, and the two need opposite treatments.
Try it yourself
Think about the last time you were ill. Could anyone else have caught it? That answer sorts it into one of the two kinds.