What is the likely diagnosis if a 1-month-old infant has increased non-bilious vomiting and an olive-sized abdominal mass?

The likely diagnosis of pyloric stenosis in a 1-month-old infant presenting with increased non-bilious vomiting and an olive-sized abdominal mass is supported by the characteristic features of this condition. Pyloric stenosis occurs when the pylorus, the opening from the stomach into the small intestine, becomes narrowed due to hypertrophy of the pyloric muscle. This results in difficulties for gastric contents to pass into the intestine.

Non-bilious vomiting is a hallmark of pyloric stenosis, as the obstruction occurs before the bile duct and thus bile is not present in the vomit. The vomiting typically appears shortly after feeding and can often lead to dehydration and electrolyte imbalances if not addressed. The "olive-sized" mass refers to the palpable firm mass often felt in the right upper quadrant of the abdomen, which represents the hypertrophied pyloric muscle.

In the context of the other options, gastroesophageal reflux generally presents with different vomiting characteristics and does not typically cause such a mass. Milk protein allergy could lead to vomiting as well, but it would not specifically result in an olive-sized abdominal mass or non-bilious vomiting. Viral gastroenteritis usually presents with diarrhea and can include bilious vomiting if significant gastric content stasis occurs,