There are some things such as cigarette smoke and excessive alcohol consumption that will definitely harm our human cells. But our cells are constantly being damaged just by being alive – through changes that occur in our genetic material. Most of these changes do not cause problems, but sometimes they do. This is one reason why older people have a higher likelihood of cancer – because they have a higher number of total changes to their genetic material. In terms of exposure to harmful bacteria this is more difficult beyond taking sensible precautions like cooking food properly. Most bacteria are actually not harmful and there are millions of friendly bacteria in and on us which we could not live without.
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