Viral Gastroenteritis: This is the most common cause of stomach ache in adolescents, often presenting with nausea, vomiting, diarrhea, and abdominal cramps. The high incidence of viral gastroenteritis in the population and its typical presentation make it the leading consideration.

Functional Dyspepsia: A common condition characterized by recurring upper abdominal pain or discomfort not associated with bowel movements, which can be related to eating or worsened by eating. It's a frequent cause of stomach ache in teenagers due to stress, dietary factors, or other non-organic causes.
Constipation: Although often overlooked, constipation can cause significant abdominal pain and discomfort. Changes in bowel habits, dietary factors, or decreased physical activity can contribute to constipation in adolescents.
Irritable Bowel Syndrome (IBS): Characterized by abdominal pain associated with changes in bowel habits (diarrhea or constipation), IBS is a common gastrointestinal disorder in adolescents that can cause recurring stomach aches.

Appendicitis: Although less common, appendicitis is a medical emergency that requires prompt surgical intervention. It typically presents with severe abdominal pain that initially may be diffuse or around the navel and then localizes to the lower right abdomen. Missing this diagnosis can lead to perforation and severe complications.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic abdominal pain, changes in bowel habits, weight loss, and other systemic symptoms. Early diagnosis and treatment are crucial to manage the disease and prevent complications.
Peptic Ulcer Disease: Gastric or duodenal ulcers can cause severe, burning abdominal pain, often related to eating. While less common in adolescents, it's essential to consider, especially if there's a history of NSAID use or Helicobacter pylori infection.

Gastric Volvulus: A rare condition where the stomach abnormally twists, leading to severe abdominal pain, nausea, and vomiting. It requires urgent medical attention.
Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially causing bowel obstruction. It's rare in adolescents but can present with severe abdominal pain, vomiting, and bloody stools.
Hernias: Although more common in other age groups, hernias (like inguinal or umbilical hernias) can cause abdominal pain and discomfort in teenagers, especially if they become incarcerated or strangulated.