William J. Klish, M.D., is Professor of Pediatrics, Head of Pediatric Gastroenterology at Baylor College of Medicine and Chief of the Nutrition and Gastroenterology Department at Texas Children's Hospital in Houston. Dr. Klish has served as chair of the Committee on Nutrition of the American Academy of Pediatrics.

Q: My 5-month old spits up regularly after his bottle feedings. What causes this, and do I need to worry he's not getting enough to eat?

A: Spitting up is very common in infants When babies are born the muscle in the valve between the stomach and esophagus is weak. This allows milk from the stomach to be pushed up into the esophagus and occasionally into the mouth, resulting in in spit up. As the baby ages, the muscle becomes stronger; Anywhere from between 4 and 12 months of age the problem may subside.

Spitting up becomes a concern if the baby is not growing well due to lack of nutrition, getting recurrant pneumonia due to aspirating (breathing in) their vomit, or getting irritation to the esophagus which can cause flecks of blood in spit-up and poor feeding. Beyond this, spitting-up is more of a problem for parents than for baby because it's messy.