Signs and Symptoms of Mast Cell Activation Syndrome (MCAS)

Medically reviewed by Jurairat J. Molina, MD

Mast cell activation syndrome (MCAS) is a condition in which mast cells—a type of white blood cell that plays a key role in the immune system—release excessive amounts of histamine and other inflammatory substances in response to ordinarily harmless triggers, such as foods, temperature changes, medications, stress, sunlight, or exercise.

Mast cells are in tissues throughout the body, including the skin, gastrointestinal, cardiovascular, neurological, and respiratory systems. Normally, mast cells detect and respond to threats like infections and injuries by releasing inflammatory substances called "mast cell mediators" to fight off the threat and promote healing.

With MCAS, mast cells activate and release these mediators frequently or excessively after exposure to one or more triggers, leading to severe symptoms that can affect many body parts and systems. The factors that contribute to MCAS episodes and the severity of symptoms vary from person to person.

MCAS symptoms may be chronic and frequent or come and go in recurrent episodes. People with MCAS may experience mild symptoms for an extended period before experiencing symptoms that worsen in frequency and severity.

Skin Symptoms

The skin has high concentrations of mast cells because it's your body's first line of defense against bacteria, viruses, and other environmental threats. Most people with MCAS experience dermatologic symptoms that may include:

• Pruritis (itching): Itchiness may be intense and widespread

• Urticaria (hives): Raised, red welts on the skin's surface

• Flushing: Sudden reddening of the face, neck, and chest due to dilated blood vessels and increased blood flow to the skin

• Angioedema (swelling): Swelling under the skin around the lips, eyes, hands, feet, and throat

• Dermatographism: Scratching or pressing on the skin causes hives (raised, red welts)

Gastrointestinal Symptoms

Gastrointestinal (GI) symptoms affect up to 80% of people with MCAS and can include:

• Abdominal pain or cramping

• Bloating

• Diarrhea

• Cyclical or chronic nausea and vomiting

• Dyspepsia (indigestion)

• Heartburn

• Dysphagia (difficulty swallowing) 
  

Respiratory Symptoms

MCAS symptoms affecting the respiratory system (lungs and airways) may include:

• Runny nose

• Nasal congestion

• Shortness of breath or difficulty breathing

• Wheezing (whistling sounds during breathing)

• Cough

• Throat swelling 
  

Cardiovascular Symptoms

Mast cell activation can affect the heart and blood vessels, leading to cardiovascular symptoms such as:

• Rapid heart rate

• Heart palpitations

• Low blood pressure

• Fainting

• Chest pain or discomfort

Musculoskeletal Symptoms

MCAS can cause symptoms that affect the musculoskeletal system, including muscles, bones, joints, ligaments, and tendons. Many people with MCAS experience these symptoms daily. They include: 

• Joint pain

• Muscle aches

• Bone pain

• Osteoporosis or osteopenia (loss of bone mass)

Neurological Symptoms

MCAS can affect the nervous system, leading to a wide range of cognitive difficulties, psychiatric disorders, and mood changes, including:

• Headaches

• Cognitive dysfunction, which may include brain fog, difficulty concentrating, or memory problems

• Dizziness

• Anxiety, depression, or panic attacks

• Insomnia (difficulty falling asleep or staying asleep)

• Mood swings or irritability

• Neuropathy (nerve damage), which may feel like numbness and tingling

• Tinnitus (ringing in the ears)

• Excessive daytime sleepiness

Genitourinary Symptoms

Genitourinary symptoms are symptoms that affect your urinary or reproductive system. MCAS symptoms include:

• Frequent urination

• Urinary urgency, a sudden and strong urge to urinate

• Painful urination

• Infertility 
  

In women and people assigned female at birth, MCAS may also cause:

• Menorrhagia: Menstrual bleeding that lasts seven days or more

• Dysmenorrhea: Painful uterine cramping during your menstrual cycle

• Miscarriage: Pregnancy loss  
  

In men and people assigned male at birth, MCAS may cause:

• Prostatitis: Inflamed, painful prostate

• Sexual dysfunction: Difficulty getting or maintaining an erection

Systemic (Bodywide) Symptoms

Generalized symptoms of MCAS that are not limited to one organ or body system include:

• Fatigue

• Sweating

• Appetite changes

• Unintended weight loss or gain

• Slow wound healing times

• Weakness

MCAS and Anaphylaxis

People with MCAS have an increased risk of experiencing anaphylaxis—a severe allergic reaction. Anaphylaxis symptoms develop suddenly and can quickly become severe and life-threatening, requiring immediate medical treatment. Symptoms include:

• Abdominal pain, nausea, vomiting 
  

• Chest tightness, heart palpitations

• Difficulty breathing or swallowing

• Nasal congestion

• Hives 
  

• Slurred speech

• Facial swelling (including around the eyes and the tongue)

• Loss of consciousness
  

Symptoms in Children

MCAS is more common in adults than children, but children can also develop the condition. When symptoms of MCAS first appear during childhood or adolescence, they often persist into adulthood.

Symptoms of MCAS in children are similar to those in adults. If you suspect your child may have MCAS, see a healthcare provider to discuss your concerns.

When to Contact a Healthcare Provider

MCAS symptoms vary from person to person, though they generally involve two or more body systems at once. Reach out to a healthcare provider if you have persistent or concerning symptoms, symptoms that affect more than one body system, or symptoms that make daily life, work, or sleep difficult.

Schedule an appointment with a healthcare provider if you experience:

• Persistent or recurring skin symptoms like itching, hives, flushing, or swelling

• Ongoing digestive issues like abdominal pain, nausea, vomiting, diarrhea, or constipation

• Difficulty breathing, wheezing, or persistent cough

• Recurrent headaches, brain fog, fatigue, or dizziness

• Frequent urination or urinary urgency
  

Seek immediate medical attention if you experience signs of anaphylaxis, which may include:

• Sudden, severe swelling of the face, lips, tongue, or throat

• Wheezing, shortness of breath, or difficulty breathing that rapidly worsens

• Fainting or loss of consciousness

• Chest pain, chest tightness, or rapid heart rate (over 100 beats per minute)

• Sudden, severe diarrhea, nausea, or vomiting

Questions To Ask Your Provider

Preparing a list of questions to ask your healthcare provider can help ensure your questions and concerns are addressed during your appointment. Consider asking:

• Are my symptoms related to MCAS, or could another condition be the cause?

• What tests will I need to confirm a diagnosis of MCAS?

• My skin itching and fatigue have been bothersome lately. What can I do to manage these symptoms?

• Do you recommend any lifestyle changes that might help manage my symptoms? 
  

A Quick Review

Mast cell activation syndrome (MCAS) is a disorder in which mast cells release excessive inflammatory chemicals in response to a normally harmless trigger. People with MCAS can experience symptoms that affect the skin, gastrointestinal, respiratory, cardiovascular, musculoskeletal, neurological, and genitourinary systems.

Symptoms vary from person to person but may include itching, hives, shortness of breath, digestive issues, fatigue, and brain fog. See a healthcare provider if you experience persistent or concerning symptoms of MCAS. Early diagnosis and treatment can help manage symptoms and improve your quality of life.

Frequently Asked Questions

What foods trigger MCAS?

Food triggers can vary from person to person, but the foods that most commonly trigger MCAS include alcohol, shellfish, food preservatives, flavorings, dyes, tomatoes, chocolate, pineapples, and food containing monosodium glutamate (MSG).

Can MCAS be cured?

There is no cure for MCAS, but treatments (e.g., medications) and lifestyle modifications can help manage symptoms and lower the risk of MCAS episodes (symptom flares).

How can I calm my mast cells naturally?

While research is ongoing, some evidence suggests quercetin, an antioxidant found in certain fruits and vegetables (e.g., apples, onions, berries, broccoli), may help stabilize mast cells and control inflammation.

Some people with MCAS may benefit from eating a low-histamine diet, but there is limited evidence of its effectiveness. Consult a healthcare provider before trying dietary supplements or changing your diet to manage MCAS. 

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