Gastroesophageal Reflux Disease (GERD): This is often the most common cause of frequent nausea, especially if it's accompanied by symptoms like heartburn and regurgitation. The stomach acid flowing back into the esophagus can cause nausea.

Viral Gastroenteritis: Commonly known as the stomach flu, this condition can cause nausea, vomiting, and diarrhea. It's highly contagious and often spread through close contact with someone who's infected.
Food Poisoning: Consuming contaminated or spoiled food can lead to nausea, vomiting, and stomach cramps. The symptoms usually appear within hours of eating the offending food.
Pregnancy: Morning sickness is a classic symptom of early pregnancy, characterized by nausea and vomiting. While it's called "morning" sickness, it can occur at any time of day.
Migraines: Some people experience nausea and vomiting as part of their migraine symptoms. The nausea can be severe and may be accompanied by sensitivity to light and sound.

Appendicitis: Although nausea can be a symptom of appendicitis, it's often accompanied by severe abdominal pain, especially in the lower right quadrant. Missing this diagnosis can lead to a ruptured appendix, which is a medical emergency.
Pancreatitis: Inflammation of the pancreas can cause severe nausea and vomiting, along with abdominal pain. It requires immediate medical attention to prevent complications.
Intestinal Obstruction: A blockage in the intestines can cause severe nausea and vomiting, along with abdominal pain and constipation. This is a medical emergency that requires prompt treatment.
Brain Tumors: In rare cases, nausea can be a symptom of a brain tumor, especially if it's causing increased intracranial pressure. Other symptoms might include headaches, vision changes, and seizures.

Cyclic Vomiting Syndrome: A rare condition characterized by recurring episodes of severe nausea and vomiting. The cause is often unknown, and it can be difficult to diagnose.
Gastroparesis: A condition where the stomach muscles are weakened, leading to delayed emptying of food from the stomach. It can cause nausea, vomiting, and feeling full after eating only a small amount of food.
Superior Mesenteric Artery Syndrome: A rare condition where the duodenum (the first part of the small intestine) is compressed between the abdominal aorta and the superior mesenteric artery. It can cause nausea, vomiting, and abdominal pain after eating.