Carcinoid tumors are sometimes the cause of flushing episodes (see carcinoid syndrome), but there are many other etiologies of flushing.

Noncarcinoid flushing is characterized by episodic erythema and warmth of the head, neck, and arms. Flushing is caused by rapid vasodilation in the skin, typically mediated through either the autonomic nervous system or vasoactive molecules.

Flushing can be constant or episodic. Vasoactive mediators, either endogenous or medications, are usually the cause of episodic flushing. Flushing due to autonomic causes is often associated with sweating. Patients with persistent flushing may have fixed facial erythema with telangiectasias. Rarely, patients can develop a cyanotic change, which is caused by large cutaneous blood vessels that contain slow-flowing deoxygenated blood.

Initial history and physical is important and may give the diagnosis before any tests are ordered. Some common causes that do not require additional testing include rosacea, fever, emotional flushing, menopause ("hot flashes"), anaphylaxis, diet, or medication or alcohol (see drug-induced flushing reaction).

Anaphylaxis is a can't-miss diagnosis and should always be in the differential diagnosis of a patient presenting with acute hypotension, difficulty breathing, and angioedema.

Mastocytosis (urticaria pigmentosa, mastocytoma, diffuse cutaneous mastocytosis) is an important diagnosis to consider in children with flushing, especially if these flushing episodes are associated with hypotension.