Histamine Intolerance (HI) / Mast Cell Activation Syndrome (MCAS)

Remember, the information on my website, podcast, Instagram, and any other ways I communicate and/or produce content is educational information only and not medical advice. Always check with your qualified medical professional before making any changes to your treatment plan for endometriosis or any other health problems. See my full disclaimer here.

Note: all of this is my layperson’s understanding of these conditions, and I’m not an expert in them.

HI and MCAS are separate co-conditions from endometriosis and not everyone with endometriosis has these conditions. However, I’ve come across many people who have endometriosis and HI or MCAS. Mast cells do play a role in endometriosis but I don’t have enough knowledge on the topic to comment on it.

Dealing with MCAS symptoms, which began 6 months after my excision surgery and 9 months after losing my ovary, has been extremely difficult. Not to mention, shocking! I had no idea a person could react – and so severely – to countless foods, products, and normal activities. Unfortunately, this resulted in me having to overhaul my entire life (again, after having once done that for endometriosis), which was devastating and overwhelming, especially since I was only 6 months post-op when the symptoms began and still healing both physically and emotionally from surgery. The grief and fear I felt at the onset of this condition was immense.

It felt completely hopeless, but 2 years later, I managed to mostly figure out what was wrong, lessen my reactions, and even bring back pieces of my life that I had to cut out. Not everything, but enough that I don’t feel anymore like my life was reduced to the bare bones. And now it’s been 4 years since onset: I still have a bunch of symptoms but it’s like 20% of what it was!

If you’re suffering right now, I’m rooting for you.

Histamine intolerance can occur when a person has an excess of histamine in the body and/or the body is unable to effectively break down histamine. 

It’s often described as a bucket that fills up little by little (from food, stress, pollen, etc) and once it overflows, you have symptoms. When your bucket is full/your histamine load is high, you often have triggers that you didn’t react to when your bucket was lower.

Histamine is found in varying quantities in food: some foods are high in histamine, while other histamine liberators, meaning that they can trigger histamine release when you ingest them. Your body also makes histamine too! Histamine is important for various bodily functions and there are 4 types of histamine receptors located all over our bodies.

The body normally breaks down histamine: for example, the DAO enzyme helps break down histamine in the gut. If your body isn’t breaking down your histamine as it normally should, due to low/impaired DAO production or something else, this contributes to your rising histamine load.

Some contributing factors to histamine intolerance can be ingesting too many high histamine foods, gut infections (some bacterias can produce histamine), interplay of hormones with histamine and DAO, having impairment of histamine breakdown pathways due to genetics or nutrient deficiencies, etc.

Mast cell activation syndrome is when mast cells, which are involved in the body’s allergy response, are overactive and release inflammatory molecules at inappropriate times.

Triggers can include:

  • food/drinks
  • supplements
  • fragrances
  • cleaning products
  • personal hygiene products/skin care (makeup, soap, hairdye, etc)
  • temperature
  • stress
  • excitement
  • exercise
  • vibration
  • sex
  • exercise
  • medicines 
  • and more

Symptoms can include:

  • headache, difficulty concentrating, brain fog, forgetfulness, anxiety/panicky feeling, insomnia, lightheadedness, tinnitus, vertigo
  • hives, flushing, swelling, sweating, dry eye
  • dry throat, hoarseness in voice, sneezing, runny nose, watering eyes, cough
  • diarrhea, constipation, bloating, nausea, abdominal pain
  • hot/cold flashes, racing heart
  • burning mouth, numbing or tingling in face or extremities
  • fatigue, urinary symptoms, muscle pain, bone pain
  • anaphylaxis
  • and more!

You don’t need to have all of those symptoms, and there are many more symptoms not listed here!

In my case, my symptoms started with food – I started having hives and swelling in my face. A few weeks later, this started happening with skin care/personal hygiene products too. By 2-3 months from the first onset, I had an array of symptoms like migraines, racing heart, insomnia, vertigo, tinnitus, running nose/sneezing, and soooo much more. By 6 months later, I was reacting to literally all the triggers I listed above and had 90% of the symptoms I listed above.

Histamine intolerance and MCAS are not the same thing.

A person can have one of these, or both of these. Many of their symptoms overlap, but MCAS symptoms may (but not always) be more severe, have a very quick onset after the trigger exposure, be in multiple body systems, include anaphylaxis, have a broader range of triggers than HI (especially beyond just high histamine foods), and/or more. Here’s a helpful article if you’re trying to differentiate which one you may have.

Getting diagnosed

There are different schools of thought for diagnosis.

“The definition of MCAS after the Vienna consensus is based on three diagnostic criteria that have to be fulfilled before the diagnosis of MCAS can be established: 1. typical (MCA-related) clinical symptoms; 2. an event-related increase in serum tryptase above the individual’s baseline tryptase (sBT)… and 3. response to drugs directed against MCA or the production or effects of MC mediators.” [(1) Source: Selecting the Right Criteria and Proper Classification to Diagnose Mast Cell Activation Syndromes: A Critical Review]

However, a small group of MCAS practitioners have come up with broader criteria for MCAS [Diagnosis of mast cell activation syndrome: a global “consensus-2]:

  1. more symptoms are included (and the patient doesn’t need to have anaphylaxis)

  2. broader range of elevated mediators: tryptase, histamine, prostaglandin D2, heparin, chromogranin A, etc (and the patient doesn’t have to have elevated tryptase)

  3. as far as I know, this is still similar to the stringent criteria needing a response to MC stabilizers or H1/H2 histamine blockers, etc

I don’t meet the criteria for the Vienna consensus because my typtase is normal. However, I have elevated chromogranin A, which doubled in levels from baseline when I was flaring. My doctor follows the Vienna consensus and told me while I don’t meet the criteria for MCAS (even though I meet the broader criteria), that I definitely have “dysautonomia with a mast cell component”, which we are treating exactly the same way as if it were an official MCAS diagnosis.

It’s important to rule out any other conditions that could be causing symptoms.

These could be things like:

  • neurological conditions like multiple sclerosis, dysautonomia

  • endocrine issues like thyroid disease

  • hormonal like low estrogen, low progesterone, or low testosterone; perimenopause, menopause

  • mental health conditions like anxiety or depression

  • digestive like inflammatory bowel disease, gut infections

  • skin issues like rosacea, contact dermatitis

  • and more

“…A number of conditions and disorders can mimic symptoms of MCA or MCAS. These conditions have to be considered in each case, especially when MCAS criteria are not fulfilled.” [(2) Source: Doctor, I Think I Am Suffering from MCAS: Differential Diagnosis and Separating Facts from Fiction]

Many allergists are not familiar with MCAS, and/or have never heard of histamine intolerance.

It’s important to see an allergist who is knowledgeable in MCAS if you suspect you have it. The first allergist I saw ran an allergy panel, said I wasn’t allergic to anything, and sent me on my way!

Additionally, since many times people have symptoms in different body systems, they may see a cardiologist for their racing heart, a dermatologist for their skin rashes, a psychologist for their anxiety, etc. It can take time to realize that your symptoms are seemingly connected and possibly from HI or MCAS.

Contributing factors to MCAS

As mentioned above, I don’t have elevated tryptase levels, which is what I was lacking to get an official MCAS diagnosis under the Vienna criteria. Do I actually have MCAS or do I just have different conditions that came on at the same time which mimic MCAS symptoms and are responsive to antihistamines? At this point, I don’t know. I’m approaching it like it’s MCAS, my doctor thinks there’s a mast cell component, and in MCAS support groups, I’ve learned so much from people with official MCAS diagnosis and people (like me) with suspected/assumed MCAS.

There can be multiple contributing factors to MCAS or MCAS-like symptoms. I’ve managed to find several of mine, and after working on them, my symptoms have diminished greatly and I don’t have as many triggers as before.

Here’s my personal contributing factors that I know of so far:

Remember, these are personal to me, but I list them here to show that addressing MCAS or MCAS-like symptoms may need a multidisciplinary approach.

Low hormone output/perimenopause

Many people assigned female at birth start having HI or MCAS or increased allergies during perimenopause. My symptoms came on about 9 months after losing my ovary at 34.

The more I learn about perimenopause, the more I see that many of the symptoms I currently have and attribute to MCAS overlay with perimenopause symptoms, such as:

  • insomnia
  • heart palpitations
  • voice changes/hoarseness
  • increased allergies
  • histamine problems
  • hot flashes
  • anxiety/panic feeling
  • tinnitus, dizziness
  • headaches
  • and more

Your hormones can play a role in histamine and mast cells [The Curious Link Between Estrogen, Mast Cells, and Histamine].

I started oral micronized progesterone and it made a big difference in my insomnia, anxiety/panic feeling, and food reactions.

Two years later, I started testosterone gel after testing low in testosterone, and within 2 months I stopped having hot flashes, that awful anxiety/panic feeling, POTs-like symptoms, and headaches/dizziness after eating.

If you had a sudden onset of symptoms and you:

  • had one or both ovaries removed
  • had a hysterecomy (even if you kept your ovaries)
  • are AFAB and 35 or older

please consider that your symptoms could be perimenopause or menopause symptoms. We are not taught body literacy and not enough doctors – even gynecologists – can recognize the symptoms of peri- and menopause, which is so much more than hot flashes! Resources and info on HRT on my website here.

SIBO and gut dysbiosis

Some species of gut bacteria can release histamine, and gut infections like SIBO can reduce DAO (an enzyme that breaks down histamine in the gut).

I did a comprehensive stool sample which showed gut dysbiosis as well as giardia. There’s criticisms about these kinds of stool samples so this may or may not have been necessary to do, but it led to me taking 2 months of herbal anti-microbials based on the results. In doing so, my MCAS symptoms of anaphylaxis and racing heart disappeared! My insomnia also improved and I could actually sleep a few hours at night (compared to before, where the only time I could fall asleep was passing out after being awake for 2 days straight.) My naturopath then suspected I had SIBO due to my clinical symptoms, risk factors, and positive response to the anti-microbials. We decided to do a different set of herbal anti-microbials for a few more rounds.

Interestingly, a few months after I treated my suspected SIBO, my 20 years of fibromyalgia pain went away as did my interstitial cystitis pain.

More info on SIBO and gut dysbiosis on my website here.

I worked with a naturopath for SIBO and while I had a really helpful experience, this doesn’t negate that there’s a lot of non-evidenced based testing and science among this type of medicine. If you’re thinking about working with a functional medicine doctor or naturopath, see my page here.

Having a “dysregulated” nervous system

My nervous system was in a state of hyperarousal: my body went into “fight or flight” for the littlest thing, and stayed there much longer than necessary. In addition to the childhood trauma and 16 years of trauma of having endo, the 2 surgeries I had 6 and 9 months prior to my MCAS symptom onset were incredibly traumatic. I noticed the tiniest amount of stress sent my symptoms through the roof.

At the onsite of my MCAS symptoms, I’d already been meditating daily since 8 years prior (which included yoga, qigong, chanting, body scanning, and visualization), and I’d done CBT for distorted thought patterns and swapping out my self-critic for a loving, compassionate inner voice. While I had learned self-awareness and important coping methods, I was still seemingly back into what felt like a state of ongoing “fight or flight” or sympathetic nervous system activation.

  • I used the Curable app for a year. This helped me to find safety in my body, calm my fight-or-flight response, and address repressed emotions and tendencies like perfectionism which were keeping my body hypervigilent and in a state of “danger”. My review here.

  • I’m halfway through the Gupta Program for limbic retraining. The concept is similar to Curable on helping retrain the brain: to stop thought patterns around my symptoms, and bring in an imagined feeling of wellbeing to my body during flares. I like the course so far and after 3 months see that I no longer am getting anxious around uncertainties or negative life changes that in the past would have sent me into a tizzy. I’ll write my review when I finish the course, which I’m doing the course with a non-desperate attitude: if it helps my symptoms, great. If not, at least it’s another tool in my box for living better with them.

Food triggers like histamine and others

Going on a low histamine diet did wonders for me. For about 6 months, I was ultra-low histamine because I had immediate, serious reactions whenever I ate food, even foods that are low histamine. I only ate once a day (when I got home from work) because otherwise I wouldn’t have been able to hold a job with all the symptoms food produced. Having such a limited diet definitely affected my mental health, but I didn’t know any other way to help reduce the intolerable onslaught of symptoms in order to stay employed.

After treating suspected SIBO, my symptoms drastically improved and I was able to eat more foods, but on a rotating basis. With each contributing factor I’ve addressed, I’ve been able to bring back more variety into my diet. I’m now able to eat many more foods in moderation, and in combination. As time goes on, I can even tolerate the highest histamine foods (like fish) in small amounts. However, I also react to several foods that are considered low histamine, so it’s not just histamine that is a problem for me, but I’m not sure if it’s oxalates or salicylates or something else.

Something that’s helped is buying frozen fruits and veggies, and eating a spoonful of a different one alongside each meal (not for the full meal, but in addition to my meal). This has been helping me expand the foods I can eat while limiting my reactions to my trigger foods. It also helps me feel more emotionally satisfied with my meals. I talk about tips for replacing foods vs restricting them, and identifying food triggers here.

Limiting my exposure to products

I basically cut out most skincare and cleaning products and only use the necessities. This is something that I still haven’t been able to reintroduce even 4 years later. Still no nail polish, hair dye, face lotion, etc for me. I now use an N95 when dusting, cleaning, and painting (my hobby). See my page here for more details on this.

Changing my lifestyle

My symptoms are sometimes still affected by activities like sex with my boyfriend, going in the sun, painting (my favorite hobby!), vibrations (like when trail biking), thrillers movies that put me on edge (and into fight-or-flight). For the first year while I struggled to come out of a continuous, nonstop flare, I had to change many of my activities because the symptoms they caused annihilated me.

Luckily, I’m now able to do all of these things again. On some days I have symptoms from them, on most I don’t. I try to be intentional about not doing multiple activities that affect me on the same day, and factoring in rest and flare recuperation time after an event.

There is hope

With any chronic illness, the grief that we can feel is overwhelming as we watch our hobbies, plans, and dreams get swallowed up by symptoms. When my MCAS symptoms first came on, I was already in an incredibly difficult moment of my life having just gotten diagnosed with endometriosis after 16 years, and having had major 2 surgeries within 4 months. When these new, scary, shocking, intense symptoms came on, the feelings of despair were so immense that I had intrusive thoughts of unaliving myself. It’s so important to get the mental health support we need. If you find yourself in a similar situation, please reach out to a professional or to a loved one for help.

I was very lucky to find a blog of a girl living with MCAS (I’d link it but she’s taken it down since then) which talked about how changing your diet and lifestyle in accordance to your own personal triggers can make this condition survivable, and eventually, you’ll be able to build a life around the condition. “There’s hope,” she said. And her words stuck with me through multiple episodes of anaphylaxis, dizzy spells I couldn’t stand up from, and headaches that made me forget how to speak.

For me, it felt unsurvivable, but I made it through the worst year of my life. While I still have many triggers and have to be intentional with my diet and lifestyle, I’m not having a constant reaction to everything anymore nor anaphylaxis. There are days when my symptoms spike depending on my food, the activities I do, or where I am in my menstrual cycle, but most days my symptoms are now low. If you are dealing with suspected or diagnosed MCAS, I can relate to how challenging, awful and devastating it is. Hang onto that hope, and keep looking for your contributing factors, be it gut related, genetic, hormonal, etc.


  1. Theo Gülen, Cem Akin, Patrizia Bonadonna, Frank Siebenhaar, Sigurd Broesby-Olsen, Knut Brockow, Marek Niedoszytko, Boguslaw Nedoszytko, Hanneke N.G. Oude Elberink, Joseph H. Butterfield, Wolfgang R. Sperr, Ivan Alvarez-Twose, Hans-Peter Horny, Karl Sotlar, Juliana Schwaab, Mohamad Jawhar, Roberta Zanotti, Gunnar Nilsson, Jonathan J. Lyons, Melody C. Carter, Tracy I. George, Olivier Hermine, Jason Gotlib, Alberto Orfao, Massimo Triggiani, Andreas Reiter, Karin Hartmann, Mariana Castells, Michel Arock, Lawrence B. Schwartz, Dean D. Metcalfe, Peter Valent,
    Selecting the Right Criteria and Proper Classification to Diagnose Mast Cell Activation Syndromes: A Critical Review,
    The Journal of Allergy and Clinical Immunology: In Practice,
    Volume 9, Issue 11,
    Pages 3918-3928,
    ISSN 2213-2198,
  2. Peter Valent, Cem Akin,
    Doctor, I Think I Am Suffering from MCAS: Differential Diagnosis and Separating Facts from Fiction,
    The Journal of Allergy and Clinical Immunology: In Practice,
    Volume 7, Issue 4,
    Pages 1109-1114,
    ISSN 2213-2198,


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