Hayfever, Histamine and Anti-Histamines

Image result for hayfever
I’ve recommended Haymax or simple coconut oil up your nose for years!

It is very definitely hayfever season right now and my nose is tickling away. It has been said that this is one of the worst hayfever seasons for a long while this year – however my own is the best it has ever been, hardly any so far :). I know some of you are suffering though, so here are a few things to help.

First, we have been discussing histamine generally on the Facebook groups so Christine has captured a lot of helpful bits and put it into a file for you there. I know some of you are not on Facebook so I have copied it in full for you below. Although, when you read that, you’ll see the quality of the discussions we have there! Do join!

Picture of Histo-X™Christine has also found us an excellent natural anti-histamine to go with the others mentioned in the resources below. Take a look at Histo-X, a mix of butterbur, nettle, mangosteen and ginger. You can read more about it here and get it in the UK via Amrita here – please use my name when registering and we hope it helps!

Other things to read include these two posts from Ruth at What Allergy which contain some really useful tips. First, one about the current spike:

50% more people have hay fever this year

and another giving lots of tips for tree and grass pollen hayfever:

20 things you can do to reduce hay fever symptoms

Then, this useful post from Yasmina on DAO:

How To Naturally Boost Production Of The Histamine Degrading DAO Enzyme

Our Facebook discussions and links:

Histamine Intolerance

I have picked out a few comments from various threads and put them all together here for reference. You can also read about histamine intolerance here and read the article here about how histamine intolerance can be triggered by hormones.

Micki has done a blog post about antihistamines here and for a more in depth blog post about antihistamines, read this.

Antihistamines are okay taken occasionally but not for a long period of time. They totally block all histamine, but the body needs a certain amount of histamine to function, so if the histamine is blocked, the body will react by making more and more histamine, so you could end up worse than before.

One member wrotethat’s true – I was taking anti-histamines all year round as an anti-allergy tablets for some time in the past. then I was literally unable to quit them, as every withdrawal was causing itchiness, extreme nervousness and other symptoms. meds are not the way

Another member wrote “I think you take antihistamines for a long period you get other problems – I took Clarityn one year for six months during a really bad hayfever year and ended up getting palpitations and was sent to get an ECG – I also noticed increasing weight around the tum – as soon as October came and I stopped taking them the palps went as did this horrible weight around the tum – I looked at the instructions and sure enough long term use said both of these” 

Also, antihistamines only block the histamine from causing symptoms. The body still has to break the histamine down and get rid of it, so you need good methylation for that. I take folate, B12, B2 and B6 (well I take all the B vitamins for balance) but they are the main ones for methylation. I also take TMG as a methyl donor and I find that helps tremendously.

Antihistamines (except Benadryl) also block the formation of DAO (the enzyme produced by the body to break down histamine in food) 

You would be far better off taking natural antihistamines. I have read that quercetin and bromelain are as effective as the drug antihistamines without the side effects. Also according to this article, ginseng is as effective as Benadryl. Vitamin C is also a natural anti-histamine.

There is a supplement called NeuroProtek which may help with histamine and mast cell issues.

Also, have olive oil, as this has been said to boost DAO production, as do pea seedlings grown in the dark

You also need to have adequate levels of vitamins B6 and C and copper in order for the body to make DAO (some people have gene mutations, which makes this more difficult). Also low zinc levels may allow histamine to build up (see https://draxe.com/zinc-deficiency/), and magnesium deficiency makes histamine intolerance more likely also.

The supplement DAOsin should help a lot with breaking down histamine from food (you may need more than they say though and take before each meal.) Please note that DAOsin contains rice and corn and is not suitable for vegetarians.

You need to make sure that you are not taking any histamine raising probiotics such as Lactobacillus casei, L.paracasei, Lactobacillus reuteri, and Lactococcus lactis, and instead take histamine degrading ones, such as lots of the bifidobacteria species, but particularly Bifidobacterium infantis and also Lactobacillus rhamnosus and Lactobacillus gasseri.

It is also possible that pathogens in the gut can cause histamine levels to rise in the body, especially citrobacter bacteria, e-coli and chlostridia, as well as some parasites etc, so you may like to have a gut test done to check for those.

You need to make sure that everything you eat is very fresh and freshly cooked (no leftovers). This is probably the best histamine list to go by.

Including lots of anti-histamine foods, such as blueberries and sweet potatoes and anything mentioned at this link in the diet may help, and here is a list of natural anti-histamine alternatives. Monk fruit is also an anti-histamine. See here. The more antihistamine foods you have in your diet, the better. For the Top 5 anti-histamine herbs, see here.

If I get a histamine reaction, I just have ginger tea or chamomile tea or nettle tea, as they are natural antihistamines. 

We have, what is known as, a histamine bucket and when our bucket is full, we get symptoms, so it is possible that you may react to something one day, but not the next, depending on how much histamine you have been exposed to that day.

Here is how one member lowered her histamine bucket:-

I lowered my histamine bucket by removing getting rid of all household chemicals, fragrances, essential oils and toiletries. I went down to Oliva olive oil soap and deodorant. Even stopped dying my hair. This helped me so much I was able to introduce and increase anti histamine foods and then even high histamine foods. I also meditated, breathing exercises and hypnotherapy as in Micki”a Healing Plan. I don’t have asthma but was blacking out with histamine reactions, constantly covered in hives and lost all foods for over 2 years so it’s an overall strategy for histamine rather than specifically for asthma


The henna, toiletries and make up can all add to the histamine bucket though which is currently overflowing due to puppy gate. Have you thought about some hypnotherapy with Julie?”

If your histamine problems are being caused by airborne allergens such as pollen, dust, mould etc, then you could also wear a mask or nose filters to help, and get an air purifier, such as Blue Air or a steriliser such as Airfree or here is a another suggestion from a member:-

have you tried the Medinase – light therapy done with two probes up the nose for about 4 mins – this really does work for hayfever etc. and is also known to help asthma” “I’ve got one and it does work – I do get a bit hayfever but compared to what I used to be like I’m tons better

If you want to increase IgA levels or lower histamine, listen to Mozart!!

The act of digesting itself causes histamine release (see https://healinghistamine.com/wondering-why-you-react-to-everything-you-eat/)

Don’t eat burnt foods, because they release Heterocyclic amines and histamine intolerance usually includes other amines as well.

In case it helps, another member very kindly gathered together lots of histamine/mast cell links here in Files on the TrulyGlutenFree group: https://www.facebook.com/groups/Trulyglutenfree/89700283039233 6/

Phew, that should give you plenty to go at. Hope it helps!


New Histamine Beginners Guide

The Beginner's Guide to Histamine Intolerance by [Joneja, Janice]   This time, not one of my books! Dr Janice Joneja (her of the really useful Histamine Intolerance Q&A you can see on my histamine section here) has brought out a new Beginner’s Guide which I read and reviewed last week.

I thought it was great and will be very useful when people ask me: ‘Is it HIT (histamine intolerance), allergy or MCAS?’ I shall say: read this and then come back to me!

Available as an e-book here on Amazon UK, here on Amazon US.  And you can see my mini review of it here.

Meantime, here is the intro blurb to start you off, well done Janice!

A distillation of her years of research and experience in a really easy-to-understand format – complete with suggestions for a low histamine diet.
‘For the first time in this long, exhausting, lonely journey, I finally feel like I’ve been pointed in the right direction to find answers and wellness! Thank you Dr. Joneja!!’

If you’re struggling with your health, but the doctor can’t find anything actually wrong with you, then perhaps you have Histamine Intolerance. It’s a condition with a range of unpleasant symptoms, which can include headaches, flushing, itching, hives, swollen facial tissues, racing heart, digestive problems, irritability and more.

Many doctors don’t know much about Histamine Intolerance, although it’s estimated that 1% of the world’s population suffers from it. If you’re one of them, you’ll know first-hand how distressing and frustrating the disorder can be.

Dr Janice Vickerstaff Joneja saw the misery that this condition caused sufferers, and made it the focus of her research work; she’s been studying the condition and helping patients since the 1990s.

She’s now created this easy-to-read guide—which will help you understand if you have Histamine Intolerance, and what you can do about it—with clear advice and explanations, lots of interesting real-life cases, plus diet and treatment recommendations.

If you wonder if your symptoms could be caused by Histamine Intolerance—or if you believe they are and want to know what to do about it—this book is for you.

DAO Histamine Intolerance Products: Is ARG Stronger or Not?

A few months ago, Allergy Research Group released a welcome new DAO enzyme product for helping people with histamine intolerance.

(If you don’t know about histamine intolerance and what I am talking about, do read my article Could It Be Histamine?

The product caused much confusion (with me and a few of you anyway!) because of the dosage differences with other more established products.

DAO Histaminase™ With Bioflavonoids 60 Capsules  http://www.allergyresearchgroup.com/dao-histaminase-with-bioflavonoids-60-capsules

Anyway, the label shows it has 41mg of Diamine Oxidase in it. This sounded very strong as the one I usually recommend is Sciotec’s DAOSin, which contains 4.2mg per capsule:

DAOSiN can 90 capsules  http://www.eat-all.co.uk/shop/daosin-can-90-capsules.html

This seemed very odd, so I thought I would look into it. Several months later (!), I have finally got to the bottom of it. It’s all in the way they say it on the label apparently. Here’s my conversation for you (or one of the many..)..

In effect, two ARG capsules equals 1 Sciotec! Got there with my nagging in the end!

If you open the capsules there are little beads inside, they are called pellets.
the pellets are the coated DAO
in our capsules we have 81mg Pellets
and this 81mg Pellets deliver 9000-10000 HDU
they [ARG]state on their Label 41 mg DAO (Daosin)
with 5000 HDU
so they give the weight of the Daosin pellets, they buy from us
practically, their product delivers only half of one of our Daosin capsules
You are saying that in reality, a capsule contains 2.1mg as opposed to your 4.2mg, correct?[me]
Yes right. This is the weight of the Protein extract from the porcine kidney with 7% DAO
So you have in their capsule 41mg Daosin pellets with 2.1mg Protein extract with 7% DAO
And in yours…?[me]
81mg Dao Pellets and 126mg Vitamine C. 4.2mg Protein extract with 7% DAO
It is best to look
at the HDU
histamine degrading unit
the higher the HDU the more histamine is broken down
Hope that makes some sense and allays the confusion!

Histamine Intolerance Triggered By Hormone Change?

Interesting article on histamine intolerance causing panic and anxiety today for you.

Histamine, anxiety and panic attacks

That’s helpful in itself, isn’t it, but whilst I was reading it, I picked up the fact that histamine intolerance is commonly triggered at peri-menopause, right when the hormone levels are changing yet again. This does fit in with my clinical experience that it is mostly women over about 50 who have it, but I have also seen it happen after having babies and breast-feeding as well as during puberty. Of course, men’s hormones also change at puberty and during so-called andropause, which might also explain the timing of their own developing histamine issues.

So why, two years ago, did these symptoms suddenly appear, apparently out of the blue? The answer lies in the information you provided in response to my further question: you are now 50 years of age. Two years ago you likely entered peri-menopause, or menopause, and your hormone levels, especially oestrogen and progesterone, changed dramatically. As a result, the histamine controls in your body were affected, and you developed histamine intolerance.

Does that fit in with the start of your symptoms maybe? Might be worth a think, then, if so, check your hormone levels and correct them, not forgetting your adrenals, which start to have a lot more influence on hormone production after about 40.

A clue? Hope it helps for you.

Histamine and DAO Tests Upgrade

Just a quickie to let you know that I have now managed to get one lab to do both whole blood/urine histamine and DAO (diamine oxidase) levels which will make life easier for those tracking their histamine intolerance.

We have been using Biolab for some time now for the body levels of histamine and they have recently upgraded their methodology along new research lines apparently, consequently the price has gone up. Still, I would rather we had the most efficient tests with viable results than tests that don’t help, wouldn’t you? Actually, they went up months ago and I held them down for you, but needs must now as both have gone up.

They have also started offering the diamine oxidase test so, actually, when I priced both up, it wasn’t that far off my price would be using two different labs. So, I have decided to do both tests through Biolab now. If for some reason you still want your DAO tests done by BTS, our previous lab for this, that’s fine; just ask. I really want to stay with BTS but it is simply more practical to have one lab sending your test kits out and for you to have to send them back to one lab so practicality wins out.  I have combined the two tests into a discounted Histamine Intolerance Test here for you to make life easier and that bit cheaper, too, so hope that helps.

For more info on histamine intolerance generally, do read the article I wrote here: Could It Be Histamine?

With body histamine testing, you can now do either blood or urine; both are just as viable and urine is easier, of course :). DAO is still blood.

Hope that helps.


Could It Be #Histamine?

Yay – my latest article has just been published by the lovely FoodsMatter people. This time, I am looking at a more unusual type of food sensitivity – histamine intolerance or, actually to be more precise: histamine excess.

Take a look.

Could it be histamine?
Nutritionist Micki Rose looks at the symptoms, possible causes and ways to diagnose and treat histamine ‘intolerance’/excess

Could It Be #Histamine?

Yay – my latest article has just been published by the lovely FoodsMatter people. This time, I am looking at a more unusual type of food sensitivity – histamine intolerance or, actually to be more precise: histamine excess.

Take a look.

Could it be histamine?
Nutritionist Micki Rose looks at the symptoms, possible causes and ways to diagnose and treat histamine ‘intolerance’/excess


Truly #Gluten Free #AntiHistamines

 If you are anything like me, you start to dread the Summer months from about April. Despite the lovely sunshine, it brings with it the nasty P stuff: pollen! I thought I was getting away with it this year – my hayfever usually starts mid-May and I got my first symptoms 2 days ago. Milder than before but nasty none the less.

Anyway, quite a few of you have asked me about anti-histamines generally and especially since the pollen season began. I have, of course, been investigating for us all.

Conventional Medicines

These seem to be the general types and they come in various forms such as tablets, nasal sprays and inhalers etc.

  • Chlorpheniramine (Chlor-Trimeton)
  • Desloratadine (Clarinex)
  • Diphenhydramine (Benadryl)
  • Fexofenadine (Allegra)
  • Loratadine (ClaritinAlavert)
  • Cetirizine (Zyrtec)

I doubt any of these are TGF safe. However, Clarityn D 24 hour looks a possible – I am trying to get them to provide answers on derived ingredients, especially of the hypromellose and sucrose. I will report back when/if I hear.

Update: ClaritynD 24 hour is only available in the US (US people: do check it out there and let us know!). I have asked about Clarityn Rapide and the Syrups and they are supposed to be coming back to me. A week so far… I don’t hold out much hope.

Also, in desperation one day, I got hold of some Benadryl Liquid Release 10mg Caps (cetirizine). The liquid bit looked OK but the capsule shell didn’t. I had asked the manufacturer to confirm the derivations of a couple of ingredients and they came back and said that would take 8 weeks!!

8 weeks! I laughed at her and said hayfever season would be over by the time they got their act together and that was useless to me. I also made the point about the irony of not actually knowing what ingredients are made from in allergy product. Beggars belief. I asked them to find out and come back to me so at least we know. However, not to be outdone…

I thought I would split the capsule. However, the capsules are sort of all made from the liquid so that was easier said than done. Determined, I cut the (tiny) capsule in half, licked the liquid off the scissors and put the capsule halves on a white plate. Every few minutes I lifted the capsule up and licked off the liquid that had pooled there. Result: felt daft and desperate but no hayfever and no reaction :).

I did try taking a capsule the other day but I already had a migraine (drugs from dentist) so couldn’t really tell. I thought ‘in for a penny, in for a pound’. the migraine didn’t get worse and the time it went suggests it might actually be TGF. I will have to try again but am reluctant, as per..

One more update (yes, I have been busy as usual pestering people..): I have asked Boots to confirm about their Allergy Nasal Spray (like an alternative to Beconase). They have come back this morning and said that it looks grain free from their initial investigation but they are double-checking with the manufacturer. I have to say I have found Boots to be great at this and don’t balk at the heavy questioning. I have a feeling it is because the person I spoke to has a coeliac relative…

Updated Update! Boots came back today (July 29th ’13):

The supplier of the Boots Pharmaceuticals Hayfever Relief For Adults 50 micrograms/dose Nasal Spray (100 Metered Sprays) (beclometasone) ic4534514   PL 16431/0121& 0176 have confirmed that the product is free from corn/grain derivatives. 

Good news though – the new Prevalin nasal spray seems to be OK! It is a barrier type product which traps and I assume kind of absorbs the pollen/dust/airborne allergens; it’s main ingredient is bentonite clay which is extremely absorbent. This in fact makes me smile because, if you look at the ingredients, it is pretty much based on natural stuff with a few chemicals thrown in. Big Pharma catching on and cashing in?! Nevertheless, it is welcome; we need all the help we can get 😉

Here’s some info:

Prevalin™’s patented formula contains specific ingredients that uniquely deactivate pollen in the nose so it cannot irritate the nasal mucosa.

Prevalin™’s microgel formula then forms an impermeable layer on the mucosa for protection against pollen irritation.

Prevalin™ also stimulates the clearance of pollen from the body.

How does Prevalin compare

They confirmed:

..that none of the ingredients used in Prevalin are derived from any kind of grain, including corn of their derivatives. We can also confirm that the Xanthan gum is derived by bio fermentation of a sugar source, which is not from grains, corn or their derivatives.

So, I took some yesterday morning to trial it and….4 hours later, no migraine 🙂 And still no migraine 24 hours later after several doses. It looks like it might be safe.  You can get it from usual suppliers including Boots, Tesco etc.

Update: I have found this is safe but doesn’t work for me very well. Also made my mouth very dry and felt all clogged up by it especially at night. 

HayMax Pure (approx 5ml)Don’t forget too that you can use any kind of wax type product as a barrier by smearing some around and up your nose to catch the pollen before it can get too far in. The most popular one is Haymax, made from sunflower and beeswax. The pure one with no essential oils is best in my view. I have also used coconut oil successfully although it does make your nose all shiny!

Natural AntiHistamines

For these, I have been looking specifically at the conversion of histidine to histamine in the body as I thought, if we can understand the process, we can try and do something to slow the conversion down, if you see what I mean. Here’s what I found:

Histidine Decarboxylase is the enzyme responsible for converting histidine to histamine. Catechin and other flavonoids have been shown to be potent inhibitors of histidine decarboxylase in vitro19 and in vivo.20 This action has wide clinical application (e.g., allergic conditions, peptic ulcers, inflammatory processes, other conditions where histamine is involved).

Quercetin can be used, or flavonoid-rich extracts such as those from grape seed, pine bark, green tea, or Ginkgo biloba may prove even more helpful due to their better bioavailability. In particular, the proanthocyanidins from grape seed or pine bark extracts…

I have listed suitable quercetins in the Barrier Plan and, in the TGF Master List, there are several quercetins and I think both ARG and Kirkman do both grape seed and pycnogenol (Proanthanol) – look at the Bioflavonoids section.

Update: I have been managing to take Quercetin fine. That’s a first. But still not strong enough for the hayfever for me, sadly.

We musn’t forget nature’s antihistamine either: plenty of Vitamin C (but since 99% is derived from corn, be really careful about the source of it – see the TGF Master List again for specific recommendations).

Hayfever Nasal sprayUpdate: I have discovered that Bioforce Pollinosol Spray is TGF safe. This is a herbal spray based on Luffa, which we used to sell a lot of in the dispensary days, although it was the homeopathic version. It contains:

Luffa operculata (Luffa), Ammi visnaga (Toothpick Weed),Aralia racemosa* (American Spikenard), Cardiospermum halicacabum* (Heartseed), Okoubaka aubrevillei (Okoubaka),Larrea mexicana (Chapparal) Galphimia glauca (Golden Thryallis), in an isotonic solution buffered with disodium hydrogen phosphate dodecahydrate, sodium dihydrogen phosphate dihydrate and less than 0.7% ethanol.

Of course, I checked the ethanol and they have confirmed it is from sugar beet not grain, hoorah:

all our tinctures are made from the medicinal grade alcohol, from sugar beet. The tablets are made from those tinctures, with the alcohol spun off rather than lifted with chemicals. Many people therefore find that they can tolerate them better than other ranges. Also, when the herbs are harvested from the farm, the manufacturing processes take place very soon indeed, as the herbs only have to be trundled down the track to the farm buildings rather than travel miles. So firstly no volatile ingredients are lost and secondly no fumigation/iradiation (sic)/general chemical unpleasantness is needed. Another boost for people with sensitive systems. 

I will be looking more into the Bioforce range then as a result and will of course report back.

The other main area of antihistamine action is to stop mast cell reactions.

Mast Cell Stabilizers

The key ones seem to be:

  • Cromolyn (NasalCrom – conventional med)
  • Quercetin
  • Spirulina (Spirulina spp.)
  • Stinging nettle (Urtica dioica). I have been thinking about trying nettle tea actually for a source of this.

Also, I have been investigating Butterbur, which is a traditional remedy for migraine actually, hence me looking at it, but then I read this:

Butterbur is becoming more popular for allergic rhinitis…and it is the best studied. Butterbur and the butterbur constituent “petasin” appear to decrease plasma histamine and leukotrienes.10336 They also seem to decrease priming of mast cells in response to contact with allergens.10337

Several clinical trials have evaluated butterbur for allergic rhinitis. Most studies have used a specific extract called ZE 339 (Tesalin, Zeller AG), which is not available in North America. Taking one tablet of this extract 3-4 times daily seems to significantly decrease mediators of nasal inflammation and symptoms of allergic rhinitis.7595,10336,10337,14414 Some evidence also suggests that this extract might be comparable to cetirizine (Zyrtec) 10 mg/day or fexofenadine (Allegra) 180 mg/day for reducing symptoms.7595,14414

Ooh, sounds promising…

Butterbur should be standardized to contain at least of 7.5 mg petasin and isopetasin and be UPA free (which most on the market certainly should be). UPAs are alkaloids that can be toxic and should be removed from the natural butterbur to be able to sell it. There are some concerns about this and it should say UPA or PA free on the label. I need to do some more research on this and will report on it for you asap if I find a suitable one.

A brand name similar to the one that has been studied and that is labelled UPA-free is Petadolex. I am just investigating it for us and have a couple of questions outstanding but it is looking OK so far, fingers crossed.  Petadolex 75 mg

Butterbur + 60'sSolaray also do one but they have, so far, not responded to my emails.

Homeopathic Hayfever Treatments

Homeopathics might provide a solution for us too. I thought I had found a suitable Heels remedy in Histamin Injeel ampoules but, as I was about to take it, I discovered it contains ethanol. It is about the only Heels oral vial that contains something other than sodium and water with the remedy. How annoying! Why is it always the anti-histamines they add allergens to?? Aargh. It might be OK but I am reluctant to trial it now, of course. It is sitting on my desk right this minute staring at me.

Update: I have swapped the Histamin Injeel for Euphorbium Comp. This contains luffa in homeopathic form (see above for the Bioforce herbal alternative). I have yet to try it but it has no alcohol and I am tolerating the rest of the Injeel/Comp range from the looks of it 🙂

Other than that, the best options seems to be to ask Helios or Ainsworths to make a sucrose only pillule remedy. Luffa is a good hayfever remedy we used to sell in the dispensary but they will advise the best one for you, or see a homeopath for a direct recommendation.

So, hope that brief (?) run-down of possible grain free antihistamines helps you. If I have missed any of your faves, do tell. Meantime, may all your runny noses and sneezing be mild 🙂

#Histamine Intolerance: Guest Post

Just to let you know, an interview I gave about histamine intolerance has just been published on the Low Histamine Chef blog so go and take a peek if you like.


I did actually say several times that I  can no way be called an expert on histamine issues and I have a long way to go with learning about it, but I gave my take on it anyway. The blog editor, Yasmina, decided to remove the stuff about me not being an expert, but I am telling you that anyway as some of you will know more about it than I do!

Hope it is of some help. Useful site to visit anyway if you suffer with or suspect histamine problems.

Interestingly, the lab who does the DAO histamine test for us has been teasing me that they have some more research/info on histamine and the gut to share with us soon. They are having a conference in Germany next week so I hope to find out more then. Look forward to it!

#Histamine Intolerance: Updated Histamine Tests

Just to let you know that today I have updated the Histamine Intolerance tests by combining both whole blood histamine and level of the DAO enzyme needed to break histamine down into one test. You can still get the whole histamine and DAO tests separately too if you need them.

For anyone who suspects histamine intolerance, it is best to check both blood levels and the DAO enzyme levels. This is because you could have a normal level of blood histamine BUT if your DAO enzyme levels are low, you would get the symptoms of histamine intolerance. People think they need to see high blood histamine on tests and rule out a histamine problem if levels show normal – but that could be misleading if the DAO enzymes are low. The new histamine intolerance test just makes life that bit easier – and cheaper as I have discounted it slightly for you too 🙂

Here’s some info on histamine intolerance from Allergy UK:

What is histamine intolerance?

Put simply this is an imbalance of histamine and the enzyme DAO, Diamine Oxydase (sic) in the body.  For someone with histamine Intolerance,  this deficiency means that they are unable  to break down ingested histamine quickly enough.

The consequence: Ingested histamine is broken down significantly slower and accumulates within the body. The body then reacts to the accumulated histamine with similar symptoms as for allergies, for example, with rashes, itching, headaches, diarrhoea and vomiting or abdominal pain.    It is important to know however that this does not point to an allergy, but to intolerance.