Vomiting is usually a symptom of an underlying condition and the contents and color of vomitus provides clues as to what that condition might be.

Some of the properties of vomitus and what it indicates are described below:
 

• As vomiting expels the content of the stomach, the pH of the vomitus is almost always highly acidic. The acid creates a burning sensation in the back of the throat or and roof of the mouth or nose if the vomit has passed through the nose.
• Vomit is almost always foul smelling.
• Sometimes, heaving results in vomitus with nothing in it apart from swallowed saliva.
• Vomiting after eating usually expels the contents of the stomach and therefore the undigested contents of the meal. Depending on the time of the meal and the interval between the meal and the vomiting episode, the contents and degree of digestion vary.
• Sometimes the vomitus may be streaked in blood and be a red and brown colour. This is called blood vomiting or hematemesis. Fresh blood in the vomit appears red and usually comes from the upper gastrointestinal tract. Blood that comes from the lower gastrointestinal tract usually undergoes oxidation and may appear brown in color. Clotted blood appears dark red in color and is usually seen when there is perforation of a peptic ulcer. Bleeding from the gastrointestinal tract needs to be handled as an emergency.
• Contractions of the duodenum lead to the secretion of bile in the vomitus. This gives a greenish tinge to the vomit. Severe vomiting may often yield green coloured vomit, although a bile-containing vomitus may also be yellow in colour.
• In the case of intestinal obstruction, the vomitus may contain faecal content. This is a serious condition and may require immediate medical attention and surgery.