Guest: Jessica Snyder Sachs.

Antibiotics and public santiation have led to dramatic increases in the human life span, but they have also disrupted the age-old balance between humans and the microorganisms that inhabit our environment. This morning on Focus we'll explore the "hygiene hypothesis," an argument that links the over-sanitation of modern life to increases in immune and other disorders. Our guest will be science writer Jessica Sachs, author of Good Germs, Bad Germs: Health and Survival in a Bacterial World.