The short answer
Carcinoid syndrome is a set of symptoms — flushing, diarrhea, and wheezing — caused by hormones released by a neuroendocrine tumor, usually once it has spread to the liver. Carcinoid crisis is a rare but life-threatening flare of these symptoms with dangerous blood pressure changes, and it needs emergency treatment right away.
Carcinoid syndrome is caused by hormones, mainly serotonin, released into the bloodstream by a neuroendocrine tumor.
It most often appears once the tumor has spread to the liver, because the liver normally breaks these hormones down before they reach the rest of the body.
Core symptoms are flushing (redness and warmth in the face and neck), diarrhea, and wheezing or trouble breathing.
Over time, carcinoid syndrome can also damage heart valves, so heart monitoring is often part of care.
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The full explanation.
The simple version
Carcinoid syndrome is a set of symptoms caused by hormones. A neuroendocrine tumor releases them into the blood. The main one is serotonin, along with related substances. The syndrome usually appears once the tumor has spread to the liver. Normally the liver breaks these hormones down before they reach the rest of the body. Once that step is bypassed, the hormones travel more widely and cause symptoms.
Symptoms
The core symptoms are:
- Flushing — sudden redness and warmth in the face and neck. It can look like a rash.
- Diarrhea.
- Wheezing or other trouble breathing.
Other symptoms can include belly cramps, a fast heartbeat, and low blood pressure. Over months to years, the same hormones can slowly damage heart valves. So people with carcinoid syndrome often get regular heart ultrasounds, called echocardiograms, to catch this early.
Carcinoid crisis: an emergency
Carcinoid crisis is a rare flare of carcinoid syndrome, and it is life-threatening. Symptoms surge all at once. There is intense flushing, a racing heart, and wheezing. Blood pressure rises or falls to a dangerous level. Some people become confused or faint. A crisis can happen on its own. It is also a known risk during surgery, anesthesia, or other procedures. Handling the tumor can set off a sudden release of hormones.
If you or someone you are with has these symptoms, treat it as an emergency. Call 911 or go to the nearest emergency department right away.
Do you have a known neuroendocrine tumor and a surgery, biopsy, or other procedure coming up? Tell the medical team ahead of time. They can take steps to lower the risk of a crisis. For example, they can give a somatostatin analog medicine beforehand.
Treatment
Ongoing carcinoid syndrome is usually managed with somatostatin analog medicines, such as octreotide or lanreotide. These lower hormone release, and they can ease flushing and diarrhea. Treatment also targets the tumor itself.
When to get help sooner
- Call 911 or go to an emergency department if you have a sudden, severe flare with intense flushing, a racing heart, wheezing or trouble breathing, fainting, or confusion. This can be a carcinoid crisis, and it is life-threatening.
- Call your care team the same day if you have new or worsening shortness of breath, swelling in your legs, or you feel faint when you stand up. These can be signs of heart valve damage or low blood pressure.
- Go to an emergency department if you have severe belly pain with vomiting and cannot pass stool or wind, or your belly is swollen and hard to the touch. A tumor can block the bowel, and a blocked bowel needs assessing straight away rather than in clinic hours.
- Call your care team within a day or two if flushing or diarrhea becomes more frequent or more intense than usual, or if you see blood in your stool.
Sources
Words to know
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Common questions
What causes carcinoid syndrome?
It is caused by hormones, mainly serotonin and related substances, released into the bloodstream by a neuroendocrine tumor. Normally the liver breaks these substances down before they can cause widespread effects. Carcinoid syndrome usually appears once the tumor has spread to the liver, so the hormones bypass this breakdown and reach the rest of the body.
What does carcinoid syndrome feel like?
The most common symptoms are flushing (sudden redness and a feeling of warmth in the face and neck), diarrhea, and wheezing or other trouble breathing. Some people also have abdominal cramping, a fast heartbeat, or blood pressure changes.
Can carcinoid syndrome affect the heart?
Yes. Over time, the hormones involved can damage heart valves, which can lead to heart failure if not monitored and managed. Because of this, people with carcinoid syndrome are often checked periodically with a heart ultrasound (echocardiogram).
What is carcinoid crisis?
Carcinoid crisis is a rare, sudden, and life-threatening flare of carcinoid syndrome. It causes severe flushing along with a dangerous rise or fall in blood pressure, a fast heart rate, wheezing, and sometimes confusion or fainting. It can happen on its own or be triggered by stress, anesthesia, or a medical procedure.
What should I do if I think I'm having a carcinoid crisis?
Treat it as a medical emergency. Call 911 or get to the nearest emergency department immediately. If you have a known neuroendocrine tumor and are scheduled for surgery or a procedure, tell your care team in advance so they can take steps to help prevent a crisis during the procedure.
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Last updated: 2026-08-13Next planned review: 2027-08-03
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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