Things to discuss with your doctor & what to consider before you start a low-histamine diet

Making sure you really do have HIT

Under normal circumstances your GP should be able to make a diagnosis, or send you to the right medical department that could investigate further. That would be for example a gastroenterologist if you have stomach or bowel problems, a dermatologist if you have skin problems, an allergologist or an immunologist, because they need to make sure that you don’t have any other illness.

As the information becomes more available there are more and more people who are able to get a diagnosis from doctors who have been able to read up on the subject. Only in recent years has this been possible. Some still have to really struggle to get to this point, but it is worth the struggle.

What is Histamine Intolerance in short?

Histamine Intolerance is an intolerance of histamine ingested with food. It is caused by a deficiency of the histamine-degrading enzyme diamine oxidase (DAO) or an imbalance between histamine and DAO. As far as experts are concerned it is not normally caused by genetic factors but is an acquired disease, often identified as a secondary condition to another.

Differential diagnosis

Differential diagnosis, the exclusion of possible other causes such as genuine food allergy, cross reactions, non-allergic reactions such as fructose malabsorption, lactose intolerance sorbitol malabsorption, or Coeliac Disease and the exclusion of any other illnesses and other imminently life-threatening disease such as cancer for example are of utmost importance. Some people may even have a rare disease such as mastocytosis or mast cell activation syndrome (MCAS).

HIT can be a secondary feature of all of these, but it is not a given that it will be.

There are enough complaints that look like HIT but are not and vice-versa. That is why you put yourself at risk if you self-diagnose.

Getting tested for HIT – Diamine oxidase activity and histamine levels

A test for diamine oxidase activity can bring you closer to piecing the puzzle together. If the differential diagnosis has not solved the problem then it makes sense to look into HIT.

The diagnosis is established by medical history taking and the determination of histamine and diamine oxidase before and after a 14-day histamine-free(sic) diet.¹

Details of the interpretation of results of these tests and their results can be found in the book Histamine Intolerance – Histamine and Seasickness by Reinhart Jarisch et al. (Spinger Publishing, 2015).

In the UK your GP can refer you to a lab, where they can measure the DAO activity in your blood serum and your histamine levels. Low DAO activity and high histamine levels are an indicator of HIT. Results are likely to be inaccurate if you are on a low-histamine diet when being tested.

A diagnosis of histamine intolerance is considered positive if two or more typical symptoms are present and improvement results from following a low-histamine diet and/or taking antihistamines.²

Keeping a food diary is essential so that you can track your reactions to certain foods. This is also very helpful if you start an elimination diet. This would need to be worked out with a registered dietician. You will need to find out what your threshold is in what is called a re-introduction phase.


Some scientific researchers recommend that HIT patients should take supplements of Vitamin B6 and a higher dosage of Vitamin C. Talk to your doctor about this recommendation.


It has also been recommended that as a precautionary measure HIT patients who tend to have very severe reactions, such as anaphylactic shocks, should have a small emergency pack with them at all times. This would include some form of antihistamine. This is not a replacement for the diet, as antihistamines only block histamine and don’t break it down the way DAO does. They may help reduce the symptoms, but they are not the cure.

The type of antihistamine: your doctor will need to tell you which type is suitable for your individual situation.

DAO food supplements

There are capsules containing the enzyme diamine oxidase on the market but they do not in any way replace a low-histamine diet where you need to establish your threshold. Whether a constant long-term supplementation can lead to a worsening of the condition still needs to be discussed further.

Some pharmaceuticals enhance symptoms

If you are already taking medication for the relief of symptoms or any other health reason, your doctor will need to work out if this medication is counter-productive and you need to change to another product.

There are substances used in different pharmaceuticals that have a negative effect on the DAO. For someone with HIT that means that symptoms get worse, not better. Do not change medication before you have talked to your medic, otherwise you may harm your health.

Only once you find out what is causing the symptoms in the first place can you start on the road to recovery.

Help us make a change

If you would like to help us make a change, please let us know about your experiences – positive and/or negative – via the contact page. We are not able to give any diagnosis or medical advice, but we are actively campaigning for more awareness, and your information helps us flag up the problems you are facing.

You can also copy and paste the link of this website on pages on the net wher you think this information might be helpful to other people.

Useful information about Histamine Intolerance for your GP can be found here:

¹Histamine Intolerance – Histamine and Seasickness
Reinhart Jarisch
Publisher: Springer
ISBN: 978-3-642-55446-9 (Print) 978-3-642-55447-6 (Online)

²Histamine and Histamine Intolerance
Laura Maintz, Natalija Novak (2007)
American Journal of Clinical Nutrition85 (5) p. 1185-1196