Mast Cell Activation Syndrome: Causes, symptoms and solutions

Mast Cell Activation Syndrome (MCAS) is a complex condition in which the body’s mast cells become hypersensitive, releasing excessive or inappropriate levels of chemicals such as histamine in response to triggers that are typically harmless. This overreaction can lead to a wide range of symptoms—from skin rashes and digestive discomfort to fatigue, brain fog, and even heart palpitations.

Triggers vary widely and may include certain foods, environmental exposures, or even stress. Although MCAS can be difficult to diagnose and manage, targeted nutritional and lifestyle strategies can offer helpful solutions. In this week’s blog, we will explore some of the underlying causes, common symptoms, and practical approaches to managing MCAS.

What are mast cells?

Mast cells are a type of white blood cell that play a key role in the body’s immune defence, particularly in allergic and inflammatory responses. They have normal physiologic functions such as homeostasis, tissue repair, angiogenesis, and their role in the innate/acquired immune system.i Originating in the bone marrow, they circulate in an immature form before settling in tissues throughout the body—especially in areas exposed to the external environment such as the skin, lungs and digestive tract.ii

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Once matured, mast cells act as watchful guards for signs of danger, equipped with granules rich in histamine and other chemical mediators. When triggered (appropriately by pathogens or inappropriately with MCAS) they release these substances in a process called degranulation. This release can cause blood vessels to dilate, tissues to swell, and smooth muscles to contract, all of which are part of the body’s rapid response to perceived threats.iii

Mast cells also signal other immune cells to respond; this communication helps the body react quickly to danger, but in conditions like MCAS, the response is dysregulated, triggering unnecessary or exaggerated immune responses and unpredictable symptoms.

Symptoms of Mast Cell Activation Syndrome

People with MCAS often experience a wide range of symptoms that can affect multiple systems in the body, and these symptoms may come and go without an obvious trigger.

Common symptoms include:iv

• skin reactions such as itching, flushing, or hives
• digestive issues such as bloating, nausea or diarrhoea
• respiratory symptoms like wheezing or shortness of breath
• cardiovascular symptoms – some individuals may feel lightheaded and experience a rapid heartbeat
• neurological symptoms such as brain fog and fatigue.

In more severe cases, MCAS can lead to anaphylaxis—a serious allergic reaction that requires immediate medical attention.

Mast cells typically respond to threats such as bacteria, viruses, parasites, and injuries. However, in individuals with MCAS, these cells may start reacting to additional, less harmful triggers.

Managing MCAS often requires a detective-like approach, particularly when pinpointing the factors behind symptoms. While food is a common culprit, environmental influences and even daily activities can play a significant role, making it challenging to identify personal triggers. Let’s explore some potential triggers below.

Dietary triggers for MCAS

High histamine foods

For people with MCAS, consuming these foods can overwhelm the body’s ability to break histamine down, leading to a flare-up of symptoms. Examples may include aged cheeses, fermented foods (e.g., sauerkraut, kimchi, yoghurt), cured or smoked meats, alcohol (especially wine and beer), and vinegar.

Histamine liberators

The following foods do not contain a lot of histamine but can trigger mast cells to release it – tomatoes, spinach, avocados, citrus fruits, and chocolate.

Salicylates

Salicylates are natural compounds found in many fruits, vegetables, herbs, and spices. While they are generally considered healthy, they can be problematic for some people. Foods often associated with reactions include strawberries, apples, grapes, cucumbers, peppers, and certain herbs.

Food additives and preservatives

These can irritate the gut and activate mast cells. Common ones include sulphites (in dried fruits, wine and pickled foods), benzoates (in soft drinks and sauces), artificial colours and flavour enhancers (e.g., MSG), and nitrates or nitrites found in cured meats, such as bacon.

Leftovers and slow-cooked foods

Leftovers and slow-cooked meals might be convenient, but they can be problematic too. The longer food is stored or cooked at low temperatures, especially protein-rich foods, the more histamine can build up.

Non-dietary triggers for Mast Cell Activation Syndrome

MCAS can be influenced by a wide range of non-dietary triggers too and these can vary from person to person:

Environmental and physical

Temperature changes which may include sudden exposure to heat, cold, or humidity may set off symptoms, as can intense exercisev or too much sunlight or UV exposure. Everyday allergens including pollen, dust mites, pet dander and even insect stings can all provoke a strong mast cell response too.

Chemical and medication

Medications such as NSAIDs (ibuprofen), antibiotics, and opioids can activate mast cells or interfere with how the body breaks down histamine. Perfumes, cleaning products and washing powders/detergents can be problematic too.

Pesticides and environmental toxins

Pesticides and toxins can overstimulate mast cells especially in those who have become sensitive after a major exposure or repeated low-level contact. Once sensitised, even small amounts can cause a strong response. Examples include cleaning products, mould, heavy metals etc.

Chronic infections

Certain infections can overstimulate the immune system, keeping it in a heightened state, aggravating mast cells. These include viral infections such as Epstein-Barr virus, bacterial infections like Lyme’s disease, and fungal overgrowth (candida).

Gut health issues

Imbalances in the microbiome, conditions like SIBO (Small Intestinal Bacterial Overgrowth), leaky gut syndrome, or food intolerances may exacerbate symptoms. These can all contribute to systemic inflammation and therefore mast cell activation.

Autoimmune disorders

Autoimmunity can lead to immune system confusion, where mast cells are activated inappropriately.

Emotional

Psychological stress can be a major trigger for people with MCAS. When anxious or overwhelmed, the body activates the Hypothalamic-Pituitary-Adrenal (HPA) axis, a key part of the body’s stress response system. The HPA axis releases stress hormones such as corticotropin-releasing hormone and cortisol that can directly activate mast cells and lead to symptoms, particularly in the skin, gut and brain. Additionally, chronic, ongoing stress can impair the body’s ability to return to homeostasis, keeping mast cells in an activated state.

Hormonal

Hormonal fluctuations during the menstrual cycle, pregnancy and perimenopause, can significantly impact MCAS as mast cells have hormone receptors that can influence activity.

Pregnancy

Some individuals may experience symptom relief during pregnancy due to higher progesterone levels, which have anti-inflammatory effects. However, others may see symptoms get worse, particularly in the first trimester when hormone shifts are rapid.

Perimenopause

As oestrogen and progesterone levels fluctuate, mast cell activation can become more erratic, potentially leading to increased histamine sensitivity and an increase in reactions.

Menstrual cycle

Oestrogen peaks before ovulation and during the luteal phase and can trigger mast cells to release histamine, worsening symptoms such as headaches, fatigue, or skin reactions. Progesterone, on the other hand, can have a stabilising effect.

Genetic factors

Some individuals with MCAS may have genetic traits that make mast cells more reactive. For example, mutations in the KIT gene can lead to abnormal mast cell activation, contributing to excessive histamine release and inflammation. These genetic factors do not cause MCAS alone but can increase sensitivity to triggers outlined above.

Nutritional deficiencies

Deficiencies in vitamin D, magnesium, selenium, zinc, and the B vitamins can impair immune regulation and mast cell stability.

Nutritional and lifestyle interventions to support MCAS

Targeted nutrition and lifestyle strategies can make a meaningful difference for those with MCAS. A low-histamine, anti-inflammatory diet—along with key nutrients can help to ease symptoms. Supporting the body through stress management, quality sleep, and reducing exposure to triggers further promotes balance and symptom reduction.

Support gut health

Supporting gut health is an essential part of managing MCAS as the gut is home to a large number of mast cells and plays a key role in immune regulation. When the gut lining becomes irritated or inflamed (often referred to as “leaky gut”) it can allow undigested food particles and toxins to enter the bloodstream, which may trigger mast cell activation. By focusing on gut healing strategies, you can help calm the immune system and reduce the likelihood of reactions. A healthier gut environment can also improve nutrient absorption, which is essential for maintaining the body’s natural ability to break down histamine.

Here are some key strategies to improve gut health:

Restore gut microbiome balance

Increase fibre-rich, plant-based foods: vegetables, fruits, wholegrains, nuts, and seeds. Reduce or eliminate processed foods and triggers, refined sugars, and artificial additives. If tolerated, add fermented foods or high-quality probiotics to enhance microbial diversity and improve histamine breakdown. Slowly adding prebiotic-rich foods (such as oats and bananas) can feed beneficial bacteria and promote a healthier microbiome.

Address bacterial imbalances

Consider testing for SIBO (small intestinal bacterial overgrowth) or candida overgrowth.

Support gut lining integrity

Use nutrients such as L-glutamine, zinc, vitamin A and omega-3 fatty acids to help repair a leaky gut, lower mast cell activation and unwanted immune reactions. Bone broth too (if tolerated).

Incorporate anti-inflammatory foods

Omega-3-rich fish, olive oil, turmeric, and leafy greens can help calm the gut.

Manage stress

Chronic stress affects gut function. More below.

Include specific nutrients

Certain nutrients can play a key role in managing MCAS by helping to modulate immune responses and the release of inflammatory mediators.

Quercetin vi, vii, viii, ix

Quercetin supports immune balance in MCAS through multiple mechanisms. It helps stabilise mast cells by inhibiting calcium influx, thereby preventing the release of histamine, tryptase, and other inflammatory mediators.

It also suppresses pro-inflammatory cytokines such as IL-6, IL-8, and TNF-alpha, and blocks the NF-κB signalling pathway, which is central to inflammation and mast cell activation.

Additionally, quercetin acts as a potent antioxidant, reducing oxidative stress that can trigger mast cell responses, and it lowers tryptase activity, helping to protect tissues such as the gut lining and connective tissue.

Sources of quercetin include onions, apples, berries, kale and other leafy greens, and broccoli. It is also found in supplemental form.

Vitamin C x, xi

Vitamin C supports MCAS through several key mechanisms. It enhances the activity of diamine oxidase (DAO), the enzyme responsible for breaking down histamine in the gut, thereby reducing histamine accumulation. It also lowers circulating histamine levels by promoting its degradation and limiting its release from mast cells.

Additionally, vitamin C may help stabilise mast cells, reducing their tendency to degranulate. As a potent antioxidant, it neutralises reactive oxygen species generated during mast cell activation, and it contributes to overall immune modulation, helping to prevent inappropriate mast cell responses.

Vitamin C is abundant in a variety of fruits and vegetables, most notably – acerola cherries, blackcurrants, kiwis, berries, bell peppers and green leafy vegetables. Vitamin C is heat-sensitive and can degrade with prolonged cooking so eating raw or lightly cooked is best.

Bromelain xii, xiii, xiv, xv

Bromelain supports MCAS primarily through its anti-inflammatory and tissue-protective effects. It inhibits pro-inflammatory cytokines like IL-1β and TNF-α, helping to reduce systemic inflammation.

While less studied than quercetin, bromelain may also stabilise mast cells and limit the release of histamine and other mediators.

Its fibrinolytic and anti-oedematous properties help reduce tissue swelling and vascular permeability, which are common in MCAS. Additionally, bromelain is often paired with quercetin to enhance absorption and synergistically boost anti-inflammatory benefits.

DAO Support xvi, xvii

DAO is a key enzyme responsible for breaking down histamine, particularly within the gut. When DAO levels are low—whether due to genetic factors, certain medications, gut inflammation, or nutrient deficiencies—histamine can accumulate and intensify symptoms.

Fortunately, several nutrients are known to support DAO activity and promote histamine balance. Vitamin B6 acts as a vital coenzyme in DAO synthesis and activation, while copper serves as an essential cofactor for its enzymatic function. Vitamin C not only helps degrade histamine but may also shield DAO from oxidative stress. Additionally, zinc plays a crucial role in maintaining gut integrity and supporting DAO production.

Low-histamine diet

A low histamine diet can be a helpful tool for managing symptoms This approach focuses on avoiding foods that are high in histamine, like aged cheeses and processed meats, as well as those that trigger histamine release, such as citrus fruits, alcohol and certain additives.

Low-histamine meal preparation tips

To prepare low-histamine meals, focus on fresh, unprocessed ingredients and cook meals just before eating, as histamine levels can rise over time. Minimise slow cooking, which can increase histamine, and instead use quicker methods such as steaming or sautéing. If you make extra food, freeze it immediately in airtight glass containers to prevent histamine buildup. Planning smaller batches more frequently can also help minimise leftovers and keep meals fresh.

De-stress

Finding ways to relax such as meditation, deep breathing, gentle exercise, or mindfulness can really help. Since emotional and physical stressors both impact MCAS, finding personalised relaxation strategies can make a significant difference to symptoms.

Reduce exposure to environmental toxins

Reducing exposure to environmental toxins is especially important for those with MCAS. Opting for organic food, particularly meat and dairy, can help minimise pesticide intake.

Avoid synthetic fragrances by choosing fragrance-free or naturally scented personal care and cleaning products. Improve indoor air quality by regular ventilation and by avoiding scented candles or air fresheners.

Use non-toxic cleaning alternatives or eco-certified brands, and regularly check for mould, especially in damp areas. Aim to limit plastic use by avoiding heating food in plastic containers and reduce exposure to EMFs by keeping electronics away from your bed and turning off Wi-Fi at night.

Quality sleep

Improving sleep may help ease symptoms of MCAS by helping to regulate histamine levels, reduce inflammation, and calm the nervous system.

Quality sleep supports the production of calming neurotransmitters such as melatonin and GABA, which counteract histamine’s stimulating effects.

GABA helps regulate nerve activity by reducing excitability, promoting relaxation, and balancing mood. Low GABA levels are often linked to anxiety, sleep disturbances, and increased sensitivity to stimuli. Restful sleep also lowers stress hormones like cortisol, which can trigger mast cell activity.

Additionally, good sleep promotes good gut health and immune balance—both crucial for managing MCAS. Sticking to a consistent sleep schedule, avoiding high-histamine foods in the evening, and creating a calming bedtime routine with deep breathing or gentle yoga can help. Keeping your bedroom cool and dark, limiting screen time before bed, and avoiding stimulants such as caffeine and alcohol also support better rest. Some may benefit from a magnesium supplement.

Summary

To conclude, supporting MCAS involves a comprehensive approach that includes mindful eating, specific nutrients, and various lifestyle strategies. Incorporating relaxation techniques, gentle movement, and awareness of individual sensitivities and triggers can empower individuals to manage MCAS more effectively and improve overall quality of life.

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All of our blogs are written by our team of expert Nutritional Therapists. If you have questions regarding the topics that have been raised, or any other health matters, please do contact them using the details below:

nutrition@cytoplan.co.uk
01684 310099

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Last updated on 21st May 2025 by cytoffice