It's safe to say most Americans are unaware of what it's like to live in a heavily polluted country, as in Egypt, China, or India.
Business Insider correspondent Harrison Jacobs recently visited Cairo, Egypt, which is home to 20 million people.
Jacobs says the air there is so foul one can physically sense it, through itchy eyes, a dry mouth, and even rashes.
And it's not just air pollution, which the WHO says is almost the worst in the world. Noise pollution also abounds.