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Histamine intolerance is an over-looked issue that has many health ramifications.


Signs and symptoms of excess histamine are diverse ranging from:

  • Unexplained rashes and skin hives.
  • Headaches.
  • Flushing – perhaps intertwined with potential menopause symptoms but also seen in men and younger women
  • GI issues such as abdominal pain, acid reflux/GERD, diarrhoea, constipation, bloating and known food intolerances.
  • Respiratory issues such a chronic cough or asthma, sinusitis.
  • Alcohol intolerance (especially wine), intolerance to fermented foods, and other foods high in histamine such as tinned foods, avocado, bananas and cocoa (there are many more).
  • For women, symptoms may worsen at certain times of your cycle due to a link with oestrogen which can stimulate further histamine production.

You may have been told you have ‘histamine intolerance’ or in more severe cases ‘MCAS’ (Mast Cell Activation Syndrome).    MCAS is a more complicated condition where over-activation of the nervous system and mast cell degranulation makes resolution a more complex journey, understanding underlying drivers that made someone susceptible is key.   For either condition however, timescale aside, there is much that can be done nutritionally and from a lifestyle perspective to reduce the symptoms and improve overall health.   Please note all these signs and symptoms can be due to other factors/conditions too so it is important to not self-diagnose and seek appropriate professional advise. 

Before I tell you more about some basic initial steps you can take if you know or suspect histamine is an issue its useful to know a little more about where it comes from and how it is broken down.

Where it comes from and what it does:


Histamine is a compound that has many functions in the body.

  • One source is the body’s own natural production – when you experience a cut or an infection, histamine is released from cells that are part of the immune system called mast cells and basophils as part of the body’s healing process.   This involves vasodilation of blood vessels and the subsequent swelling and redness you can see.
  • It is also a neurotransmitter released from neurons which can influence our wakefulness, cognition and circadian rhythm. However, in excess can result in irregular heart-beat and bronchoconstriction.
  • It is  is involved in regulation of certain physiological functions in the gut and also produced in the gut under certain stimuli as well as being produced in greater quantities by certain gut bacteria.
  • It is involved as part of the ‘stress’ response, not only via the adrenalin but chronically elevated cortisol can also increase the production of histamine.
  • Histamine also can come from food.

Excess histamine has been linked to long-covid as an underlying driver as well in those struggling to recover fully.

How it is broken down:

Histamine has two main pathways through which it can be broken down.

  • One is involved primarily in the gut and histamine from exogenous sources such as food using an enzyme known as DAO (Diamine oxidase).  This produced in the gut lining and if the gut lining is damaged can result in reduced production.
  • The second pathway occurs in the nervous system and lungs using an enzyme knowns as HNMT (Histamine-n-methyltransferase).  Both of the DAO and HNMT enzymes require specific nutrients (eg B12, B6, folate) to make them work.

What makes one susceptible to excess histamine and histamine intolerance:

There is a useful concept here of a bath with a plugin  – imagine we all have a bath which collects histamine but when our bath becomes full and perhaps plug that empties the bath (ie breaks down histamine) is blocked, histamine will begin to overflow, resulting in one becoming symptomatic.   How quickly someones bath fills up and what can block the plug are the individual variables that we need to work through – common considerations are:

  • Underlying sources of inflammation, possibly gut based but more systemic should also be considered which can include mould, environmental toxins, lyme and other parasites/pathogens.
  • Dysbioisis (imbalance in gut bacteria including SIBO/IMO) – certain bacteria are known to produce more of the enzyme histamine decarboxylase that converts histidine to histamine.
  • Hormonal issues in women leading to excess oestrogen production or lack of ability to break oestrogen down. Oestrogen and histamine have a sometimes unhelpful bi-directional relationship.  This is an area that is often overlooked and can worsen in peri-menopause when oestrogen fluctuates more.  If you notice a cyclical pattern to your symptoms this is worth considering.
  • Lack of appropriate nutrients to make the enzymes work.
  • Genetic susceptibility – both on the histamine enzymes specifically but also on other pathways that link across such as those relating to other key detoxification pathways.

What you can do:

  • Keep a food  and symptom diary.
  • Experiment with a low-histamine diet.   This can be quite challenging and limiting so I do not recommend doing this long-term and you may find it easier to do under professional guidance to ensure your diet remain varied and broad.   Key foods to avoid – leftovers, fermented foods, processed foods, tinned foods, avocados, spinach, aubergines, tomatoes, hard cheese, strawberries and chocolate.
  • Buy fresh food as often as possible.
  • Experiment supplementing with DAO enzymes.
  • Experiment removing foods that are histamine-blockers ie they slow down the breakdown of histamine – such black tea, green tea and alcohol.  Certain drugs can also do this but I do not recommend stopping these without medical supervision and advise.
  • Ensure you have adequate (and this may need to be at therapeutic levels which should be done under approprite professional guidance) of vitamin C, B6, B12, folate, magnesium as well as a diet high in anti-oxidants.  For some quercitin can be useful but there are certain genetic SNPs where quercitin is not useful.
  • Do anti-histamines improve your symptoms? If so this is a clue that further investigation is needed.
  • Testing – testing histamine and DAO enzyme activity is not very reliable.   What is likely to be more useful is to understand what are the underlying drivers of inflammation that have made you susceptible in the first place.   This may include both stool, blood and urine testing depending on your unique drivers that can be assessed by understanding your health timeline in detail.
  • Histamine breakdown is under quite a lot of genetic variance so genetic testing can be useful.  Please seek appropriate advice before doing this as not all DNA testing companies will give you the information you need.  Please read more here and here and contact Katherine if you want to find out more on arranging these or any other tests.
  • Pay attention to your stress levels.  Chronic stress (which most of us are subject to even if we don’t realise it) increases what is known as the HPA (hypothalamic-pituitary-adrenal) activity

Identifying histamine intolerance can be complicated by other foods and metabolic pathways that may be simultaneously impacted such as those high in FODMAPs (specific sugars implicated in other gut conditions), oxalates, salicylates and lectins and impaired detoxication.

If you want to find out more how Katherine can help support you and available tests, please contact Katherine on