Gastritis

• Nausea is an unpleasant sensation in the stomach that leads to the urge to vomit. Nausea is the symptom of a larger condition and is not a condition in and of itself.
  There are many causes of nausea. Alcohol abuse can cause acute nausea. Alcohol irritates the lining of the stomach and can lead to nausea and vomiting, as well as dizziness and intense headaches.
  There are many differing causes of gastritis, irritation and inflammation of the stomach. Coffee and other beverages with a high caffeine content can irritate the stomach and lead to nausea. The stomach flu, caused by a virus, can also cause irritation of the stomach lining and therefore nausea--as can food poisoning, which is the result of bacterial toxins. Ulcers cause nausea, too. Ulcers can simply be minor irritations of the lining, but they can also move up to becoming major defects in the stomach.
  
  

Appendicitis

• Most irritations and inflammations of the stomach pass in a short amount of time and aren't considered serious. Appendicitis, however, is extremely serious. Appendicitis is actually an inflammation of the appendix, with nausea as a byproduct. However, if left untreated, appendicitis can lead to serious internal infection and sometimes even death.
  
  

Food Allergies and Contagions

• Food allergies may cause nausea. Common food allergies that can lead to nausea are seafood, shellfish, dairy products and wheat. If you are a camper or hiker, you should know to guard against giardia, which can cause nausea, vomiting and diarrhea. Giardia is an infection caused by intestinal parasites found in feces, commonly passed on by drinking unclean water, touching an unclean surface or eating improperly cooked food. Gastroenteritis is also contagious and is passed on by contact with an unclean person, food, water or surface.
  
  

Motion Sickness

• Many people, particularly children, suffer nausea from motion sickness. Motion sickness is caused by miscommunication regarding head movement in the inner ears. Travel by train, bus, car or airplane can be quite painful for people who are susceptible to motion sickness.
  
  

Drugs and Medical Treatment

• Nausea may also be caused by side effects of medical treatments and prescriptions. Some medications may cause nausea, such as anti-inflammatories and steroids. Treatments for cancer, particularly chemotherapy, are also well known for leading to nausea in many people.
  
  

Pregnancy

• A much happier reason for experiencing nausea is pregnancy. Nausea during pregnancy is especially common during the first three months. Pre-natal nausea is caused by hormone changes in your bloodstream.