Shakespeare wrote about “the infant mewling and puking in the nurse’s arms” when describing the first stage of life.  Spitting was common then and it’s common now—affecting all babies.  But obviously some more than others.  My colleague, Dr. Ben Gold, an expert in the field, lists 3 causes:

  1. A smaller stomach,
  2. A less stretchable stomach, and
  3. The angle the stomach and esophagus make with each other is less than 90 degrees.

I add a 4th:  The strength (or tone) of the valve (the lower esophageal sphincter) between the esophagus and stomach.