What's the most deadly?

We encounter so many things on a daily basis that contributes to our decline in health without really paying  it much attention. I know everyone has their pet peeves on how they take precaution towards certain things (ex. My husband has to have meat cooked well done because he's frightened of food poisoning.) but what are your legit concerns and what do you find most threatening that's so common and undermined? Is it just paranoa or do we take things too lightly?