The signs and symptoms of carcinoid syndrome depend on which chemicals the carcinoid tumor secretes into your bloodstream.

The most common signs and symptoms include:

• Skin flushing. The skin on your face and upper chest feels hot and changes color — ranging from pink to purple. Flushing episodes may last from a few minutes to a few hours or longer.

Flushing may happen for no obvious reason, though sometimes it can be triggered by stress, exercise or drinking alcohol.

• Facial skin lesions. Purplish areas of spiderlike veins may appear on your nose and upper lip.
• Diarrhea. Frequent, watery stools sometimes accompanied by abdominal cramps may occur in people who have carcinoid syndrome.
• Difficulty breathing. Asthma-like signs and symptoms, such as wheezing and shortness of breath, may occur at the same time you experience skin flushing.
• Rapid heartbeat. Periods of a fast heart rate could be a sign of carcinoid syndrome.

Carcinoid syndrome is caused by a carcinoid tumor that secretes serotonin or other chemicals into your bloodstream. Carcinoid tumors occur most commonly in the lungs or in the gastrointestinal tract, including your stomach, small intestine, appendix, colon and rectum.

Only a small percentage of carcinoid tumors secrete the chemicals that cause carcinoid syndrome. When these tumors do secrete the chemicals, the liver normally neutralizes the chemicals before they have a chance to travel through your body and cause symptoms.

However, when an advanced tumor spreads (metastasizes) to the liver itself, it may secrete chemicals that aren't neutralized before reaching the bloodstream. Most people who experience carcinoid syndrome have an advanced cancer that has spread to the liver.

Some carcinoid tumors don't have to be advanced to cause carcinoid syndrome. For instance, carcinoid lung tumors that secrete chemicals into the blood do so farther upstream from the liver, which then cannot process and eliminate the chemicals.

Carcinoid tumors in the intestine, on the other hand, secrete the chemicals into blood that must first pass through the liver before reaching the rest of the body. The liver usually neutralizes the chemicals before they can affect the rest of the body.

What causes carcinoid tumors is unclear.

Having carcinoid syndrome can cause the following complications:

• Carcinoid heart disease. Some people with carcinoid syndrome develop carcinoid heart disease. Carcinoid syndrome causes a thickening of the heart valves, making it difficult for them to function properly. As a result, the heart valves may leak.

Signs and symptoms of carcinoid heart disease include fatigue and shortness of breath during physical activity. Carcinoid heart disease can eventually lead to heart failure.

Your doctor may recommend medications for your heart. Surgical repair of damaged heart valves may be an option in advanced carcinoid heart disease.

• Bowel obstruction. Cancer that spreads to the lymph nodes next to your small intestine can cause narrowing and kinking of your intestine, leading to a bowel obstruction.

Signs and symptoms of a bowel obstruction include severe, cramping abdominal pain and vomiting. Surgery may be necessary to relieve the obstruction.

• Carcinoid crisis. Carcinoid crisis causes a severe episode of flushing, low blood pressure, confusion and breathing difficulty.

Carcinoid crisis can occur in people with carcinoid tumors when they are exposed to certain triggers, including anesthetic used during surgery. Carcinoid crisis can be fatal. Your doctor may give you medications before surgery to reduce the risk of carcinoid crisis.