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Histamine Intolerance

This is a condition whereby the person is unwell because of an accumulation of histamine in their system. 

MCAS has only been formalised as a registered medical diagnosis in 2016, which is very recent in medical terms, but it is becoming more widely known through Long COVID. A condition called Histamine Intolerance (HIT) can co-exist with MCAS.

Doctor and Patient

Some of the symptoms of Histamine Intolerance

☑️ Skin issues


☑️ Neurological Symptoms


☑️ Respiratory symptoms


☑️ Gastrointestinal issues


☑️ Cardiac symptoms

☑️ Urological and Sexual health symptoms

☑️ Worsening allergies or sensitivities

☑️ Musculoskeletal symptoms

60-minute appointment with Dr Clare Ashby for a detailed consultation to review, examine, discuss and plan treatment.

Before the appointment, we send a detailed questionnaire which will guide Dr Ashby at the appointment and save time for more discussion which we ask you to send back before your appointment or bring with you.

At the appointment Dr Ashby will also examine you and if your symptoms indicate, she may very well request blood tests and then possibly other tests such as an ECG, if you have experienced for example palpitations. These tests are to confirm that there are no other health issues at play that need to be addressed in addition to possible MCAS. As a GP it is very important that Dr Ashby can confidently diagnose your health issue.

She will then review your questionnaire and discuss your concerns and health issues. She will then formulate a personalised management plan for you which consists of: 

  • Dietary plan and recommendations

  • advice on recommended supplements

  • medical prescribing if required

Dr Clare Ashby.png

Dr Clare Ashby


Information will also be sent subsequently by email with further recommendations and details. Although an hour sounds like a long appointment, there is much to discuss and review. This consult fee includes the cost of writing any prescriptions.


A follow-up appointment after 4 weeks is required, 45 minutes £280


The follow-up appointment is to see how the patient has responded to the treatment so far and then to make adjustments and further changes if needed.

Further information:

  • Certain supplements may be suggested and these can be purchased at the practice.

  • Other tests are sometimes requested 

  • ECG £105

  • Bowel tests (faecal samples) £213

What is mast cell activation syndrome (MCAS)?

MCAS has only been formalised as a registered medical diagnosis in 2016, which is very recent in medical terms, but it is becoming more widely known through Long COVID. A condition called Histamine Intolerance (HIT) can co-exist with MCAS. This is a condition whereby the person is unwell because of an accumulation of histamine in their system and there is a lot of overlap with HIT and MCAS and their management. 

Having these conditions suggested to you as a patient can be a bit of a relief, because it has helped you to identify why you feel unwell. However, it can also feel a burden, as it requires detective work, dietary adjustment and then supplement and medication support to get the symptoms to resolve. The essence of the treatment is to reduce how activated your mast cells are. Mast cells are like little water balloons containing histamine and other mediators that cause inflammation. 

Mast cells and histamine are a part of our immune system. An example of mast cells and histamine at work is when we are stung. Upon being stung we get a red swollen area where we were stung, the swelling, redness, itch, pain and inflammation come from mast cells releasing histamine, and other mediators into the tissue. You can imagine therefore how mast cells and histamine can cause inflammation elsewhere in the body.

MCAS patients have often suffered with mildly disordered mast cells for their whole life with a back story of some of these things: childhood asthma, eczema, recurrent tonsillitis, food sensitivities, flushing with certain foods or experiencing rashes after certain foods. Then these patients will have found they became more unwell after an acute infection or vaccine, such as Glandular Fever, Lyme, Swine flu or after a routine vaccine. Others can find they have mild inconveniences such as hayfever, or persistently runny noses, reactive skin to bites or detergents, or IBS. In addition, following trauma- physical or emotional, or other significant life event or illness can trigger this condition and then their health trajectory changes. Another big precipitant of disordered mast cells is exposure to mould in your environment. 

Doctor Using Digital Tablet

Book your MCAS / Histamine Intolerance consultation

1 hour

All these events can prime your mast cells to be more dysregulated, this means that they “pop” more readily, making you more symptomatic of the effects of whichever inflammatory mediator they are particularly releasing in you. 

MCAS can manifest itself differently in different patients.


Some of the symptoms:

Skin symptoms: rashes, hives, itchy skin, flushes after eating, reactions to bites,  to name a few.


Neurological symptoms: including headaches, migraine, brain fog, fatigue, anxiety and depression, insomnia, early morning waking feeling panicked


Respiratory symptoms: including chronic nasal congestion, chronic cough, sneezing, shortness of breath, hormonal asthma exacerbations


GI symptoms: including reflux symptoms, pain, cramping, bloating, diarrhea/ constipation, “food intolerances”, often the umbrella term of IBS has been given to a patient. 

Cardiac symptoms: including palpitations, chest pains, POTS, syncope (faintness)


Urological and Sexual health symptoms: bladder pain syndrome (for men too), chronic pelvic pain, menstrual pain, heavy menstrual bleeding, vaginal irritation after intercourse, “recurrent UTIs” but that do not show an infective organism upon testing . There is a working school of thought MCAS may have a role in endometriosis and recurrent miscarriage. 

Worsening allergies or sensitivities:

Including noticing you are becoming more sensitive to your environment; this can include things like feeling unwell or headaches with exposure to scented candles or air fresheners/ cleaning products/ washing powders/ fabric softeners. Noticing worsening hay fever. 

Musculoskeletal symptoms: the presence of muscle and joint pains- a long-standing feeling of being inflamed with painful joints and muscle aches. 

Unfortunately testing for Histamine intolerance and MCAS has complexities. For now, the diagnosis remains clinical and is confirmed by response to treatment.

In America, testing is part of the “need to prove the diagnosis” for medical insurance. However we believe that currently testing may not be very reliable and can give both false positive and negative results. Dr Ashby therefore currently uses the approach of clinical diagnosis and response to treatment to confirm the diagnosis. Whilst addressing MCAS it is usually sensible to also initially address HIT. This is because if your mast cells are dysregulated, it is likely that you have raised histamine.

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