Cesarean versus vaginal delivery: long-term infant outcomes and the hygiene hypothesis.

Concurrent with the trend of increasing cesarean delivery numbers, there has been an epidemic of both autoimmune diseases and allergic diseases. Several theories have emerged suggesting that environmental influences are contributing to this phenomenon, most notably, the hygiene hypothesis. This article provides background about the human microbiota and its relationship to the developing immune system as well as the relationship of mode of delivery on the colonization of the infant intestine, development of the immune system, and subsequent childhood allergies, asthma, and autoimmune diseases.