Mast cell activation syndrome

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at December 4, 2016
StartDiseasesMast cell activation syndrome

Mast cell activation syndrome (MCAS), which is also known as mast cell activation disorder, causes a range of symptoms that tend to come and go, of which hives are common. Generally, this condition can be controlled by medication and lifestyle changes.


Definition & Facts

Mast cell activation syndrome is a condition in which the mast cells of the body are activated inappropriately. A mast cell is a white blood cell that is derived from the myeloid stem cell and is part of the immune system and neuroimmune system. Unlike mastocytosis (in which there are a surfeit of mast cells), mast cell activation syndrome involves a normal number of mast cells; however, these cells do not function properly. The abnormal functioning leads to many complications.

This syndrome was first discovered in 1991, but it was not named until 2007. This disease was not discovered sooner because the symptoms tend to be very non-specific and hard to diagnose. All body systems can be affected by MCAS, and it usually manifests itself in childhood or adolescence. More females than males are affected by MCAS.

Symptoms & Complaints

Symptoms of MCAS are caused by having too much free floating histamine which can affect almost every part of the body. Symptoms will vary from person to person and can become worse over time.

Gastrointestinal symptoms are common. A patient may experience nausea, vomiting, diarrhea, and bloating. Abdominal pain after eating and the malabsorption of some foods and nutrients are also quite common with MCAS.

In addition, low blood pressure, which in turn can cause fatigue and episodes of dizziness or fainting, is also sometimes observed in some patients with this disorder. Many individuals also have symptoms similar to allergic reactions such as itching, hives, flushing, and wheezing.

Moreover, bone pain, cognitive impairment, sensitivity to light, anxiety, and rapid weight gain or rapid unexplained weight loss are also possible symptoms for some people. Those symptoms that seem more severe can include chest pain, the feeling that the heart is racing (tachycardia), and anaphylaxis or near anaphylaxis episodes. Again, some patients may have only a few of these symptoms while others experience many more.


The exact cause of MCAS is not actually known at this time. There may be a combination of genetic factors and environmental factors that are involved in causing this disease. Many people have periods where this disease has very mild or nonexistent symptom, and there tend to be triggers that cause symptoms to return. The triggers cause the mast cells to be overly active and degranulate more often.

For example, in some people, certain foods and drinks cause the mast cells to produce more histamines and thus symptoms. In others, insect stings may be the culprit. Pain medications such as NSAIDs, and narcotics are also often involved in the degranulation of the mast cells. Extreme temperatures, both hot and cold, strong scents, especially perfumes, and friction, pressure, or vibration of the skin can cause symptoms to be exacerbated. Finally, exercise and psychological stress can cause MCAS to become worse.

Diagnosis & Tests

Diagnosis of MCAS is very difficult because many of the symptoms are not conclusive and can be part of many other conditions. When a doctor is trying to diagnose this disease, she will be likely to ask many questions about the patient's medical history and the symptoms the patient is experiencing in an attempt to both find the cause and to rule out some other conditions. A complete physical examination will be done and may reveal some of the symptoms that the patient is experiencing such as weight gain or loss and hives, to name only a few.

Since symptoms tend to come and go, however, a patient may be feeling well on the day he visits the doctor. Blood tests will need to be performed. In addition, urine may also be tested. The blood tests may have to be repeated on more than one occasion as a baseline reading if the patient is asymptomatic on the day of the appointment. A second blood test should be done when the patient is experiencing symptoms, and at that time, the levels of tryptase and histamine will be elevated.

Treatment & Therapy

Treatment of MCAS involves a variety of medications as well as a change in diet and lifestyle for many. Since there is too much histamine released into the body, one needs to take an H1 histamine blocker, otherwise known as an antihistamine. These are commonly available over-the-counter. Many people take them to treat allergies, but they also work quite well for MCAS.

In addition, those people who suffer from digestive ailments due to MCAS may take an H2 antihistamine such as the generic ranitidine and others. These too are available over-the-counter at most pharmacies. The doctor can also give a patient a prescription for a mast cell stabilizer that can help prevent the mast cells from degranulating.

Changing the diet to avoid certain foods may also be a necessity. Foods that are high in histamines, such as fermented foods including beer and wine, will likely need to be avoided by most patients. The foods involved may be different for each individual but sulfites are a common culprit for many patients.

Activities such as exercise may produce problems for some patients and may need to be done in moderation. Treatment and lifestyle modifications will be different for each person.

Prevention & Prophylaxis

Prevention of MCAS is not really possible at this time. Since it may be hereditary, genetic counseling may be helpful for some patients. In addition as more becomes known about this disease, prevention may be possible. Moreover, once a person knows their personal triggers, it is possible to avoid them to prevent flare ups of MCAS.