Most babies spit up at least occasionally, and it's usually nothing to worry about. Sometimes, however, forceful spitting up is a sign of a more serious condition known as pyloric stenosis.

Pyloric stenosis is an uncommon condition that affects the pylorus — the opening at the lower end of the stomach that connects the stomach and small intestine. In babies who have pyloric stenosis, the muscles of the pylorus become abnormally large. This prevents food from entering the small intestine. Pyloric stenosis can lead to forceful vomiting, dehydration and weight loss. Prompt surgical treatment is important.

Pyloric stenosis is also known as infantile hypertrophic pyloric stenosis.