Can smells be bad for you? Most of us recall situations where a pungent odor—say, from a sewer, trash sitting outside, or a dirty public bathroom with a strong odor of urine—made us want to run away. “Run for your life!” you may have said to yourself. Other times, the air in a friend’s house living room was so stuffy you had difficulty breathing, or the air in your classroom smelled like dirty socks, and there were no windows to let fresh air in. Were you going to get sick?