Close up of a one-week-old baby boy with dark hair and eyes. He is wrapped in a white towel and clutching the thumb of an adult wearing a gold ring. His lips are pursed as if cooing.

Many U.S. babies may lack gut bacteria that train their immune systems

Too little Bifidobacterium, used to digest breast milk, in babies’ gut microbiomes can increase their risk of developing allergies and asthma.

Science News