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 — mainly serotonin and related substances — released into the bloodstream by a neuroendocrine tumor. It usually appears once the tumor has spread to the liver, because the liver normally breaks these hormones down before they can affect the rest of the body. Once that breakdown is bypassed, the hormones circulate more widely and cause symptoms.
Symptoms
The core symptoms of carcinoid syndrome are:
- Flushing — sudden redness and a feeling of warmth in the face and neck, sometimes with a rash-like appearance
- Diarrhea
- Wheezing or other trouble breathing
Other symptoms can include abdominal cramping, a fast heartbeat, and low blood pressure. Over months to years, the same hormones can gradually damage heart valves, so people with carcinoid syndrome are often monitored with periodic heart ultrasounds (echocardiograms) to catch this early.
Carcinoid crisis: a medical emergency
Carcinoid crisis is a rare but life-threatening flare of carcinoid syndrome. It involves a sudden, severe surge of symptoms — intense flushing, a dangerous rise or fall in blood pressure, a racing heart, wheezing, and sometimes confusion or fainting. It can happen on its own, but it is also a known risk during surgery, anesthesia, or other medical procedures, when handling the tumor can trigger 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.
If you have a known neuroendocrine tumor and are scheduled for surgery, a biopsy, or another procedure, tell the medical team in advance. They can take steps — such as giving a somatostatin analog medicine beforehand — to help lower the risk of a crisis during the procedure.
Treatment
Ongoing carcinoid syndrome is usually managed with somatostatin analog medicines (such as octreotide or lanreotide), which reduce hormone release and can ease flushing and diarrhea, along with treatment aimed at the underlying tumor itself.
Sources
- National Organization for Rare Disorders (NORD), Carcinoid Syndrome, accessed August 3, 2026.
- National Cancer Institute, Gastrointestinal Neuroendocrine Tumors Treatment (PDQ) – Patient Version, accessed August 3, 2026.
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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: 2026-08-03Next 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 verified — This page was created with AI assistance and checked against the sources listed on it. Source checking is not a medical review.
Human medical review: not completed. Cancer Explained is not clinician-reviewed, and that is a deliberate design choice rather than a gap we are waiting to close. We restate published federal guidance and cite it; the authority belongs to the source, not to us. That is why every page names where its claims come from — so you can verify us instead of trusting us. Use it to understand your situation and to ask better questions of the people treating you.
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