What Is Histamine Intolerance?

Histamine intolerance is a condition in which the body struggles to break down histamine at a sufficient rate, often due to reduced or inhibited activity of the enzyme DAO, which is produced in the small intestine. Histamine is a biochemical compound that is both produced naturally in the body and found in a range of foods.
Histamine intolerance is not an allergy, but a condition often connected to how the gut functions and how much DAO is available to break down histamine.

What Is Histamine?

Histamine is a type of biogenic amine and occurs naturally in the body, where it participates in several important functions, including:

• immune responses
  

• regulation of stomach acid
  

• nerve signalling in the brain
  

• inflammatory processes
  
  

Histamine is therefore both a signalling molecule produced by the body and something we consume through food.
When the body’s handling of histamine does not work as it should, histamine levels can influence how a person feels.

What Does “Intolerance” Mean?

Histamine intolerance is not an allergy. In an allergy, the immune system overreacts to a specific substance. In histamine intolerance, however, the issue is a reduced ability to break down histamine that is already present.

It is not caused by a fault in the immune system, but by a limitation or disruption in enzyme function.
This type of intolerance can be temporary or long-lasting and is often influenced by factors such as gut health, stress, medication use or dietary habits.

The DAO Enzyme – The Body’s Histamine Filter

The key enzyme involved in histamine breakdown is diamine oxidase (DAO). DAO is produced primarily in the small intestine and is responsible for breaking down histamine from food.

If DAO levels are low or if the enzyme is temporarily inhibited by factors such as impaired gut barrier function, medication, inflammation or microbial imbalance - histamine can accumulate and trigger various reactions.

What Can Contribute to Histamine Intolerance?

Histamine intolerance rarely has a single cause. It is more often the result of several interacting factors that affect how well the body can process and break down histamine:

• Genetic variations in enzyme activity. Some individuals have genetic differences that affect how much functional DAO enzyme is produced.
  

• Changes in the intestinal lining, for example in IBS, IBD or SIBO.
  

• Chronic stress or inflammation. Stress hormones and systemic inflammation can influence the intestinal environment and enzyme activity.
  

• Medications that inhibit enzyme function (sometimes referred to as MAO or DAO inhibitors), such as certain antibiotics, medications used for stress, depression, pain, high blood pressure and some treatments for Alzheimer’s or Parkinson’s disease.
  

• Imbalances in the gut microbiota. Changes in microbial composition can affect how much histamine is produced or broken down locally in the gut.
  

• Hormonal fluctuations. Some individuals notice varying histamine tolerance throughout hormonal cycles, such as during menstruation.
  

Histamine intolerance is therefore often complex and individual, rather than a single diagnosis with one clear cause.

How Does Histamine Intolerance Differ from an Allergy?

Although symptoms such as skin flushing, runny nose or headaches can resemble allergy-related reactions, the underlying mechanisms differ.

In allergies:

• the immune system reacts to a specific allergen.
  

• large amounts of histamine are released rapidly.
  

• reactions usually appear immediately and can be confirmed through allergy tests.
  

In histamine intolerance:

• the reaction is not immunological.
  

• the body has difficulty breaking down histamine.
  

• the issue is linked to limited DAO activity.
  
  

Symptoms often develop gradually, especially when consuming several histamine-rich foods in a short period.
There is currently no standardized test to definitively diagnose histamine intolerance, which makes detection more challenging than for allergies.

What Does the Research Say?

Research on histamine intolerance has grown in recent years, but there are still no universally accepted diagnostic criteria or treatment guidelines. Much of today’s understanding is based on a combination of scientific studies, clinical experience and individual symptom reports.

Studies have explored potential links between:

• gut microbiota and histamine balance
  

• probiotic bacterial strains and DAO activity
  

• the role of diet in influencing both histamine intake and breakdown
  

However, more high-quality studies are needed to clarify how these factors interact in practice and what determines an individual’s tolerance levels.

Much of the current knowledge therefore comes from clinical observation and patient reports rather than established official guidelines.