Highlights from this article: 

  • Histamine is a naturally occurring molecule that your immune system uses to respond to injuries. Too much histamine can cause an overreaction. 
  • Histamine intolerance (HIT) is a type of food intolerance that is suspected to be caused by eating foods that have high amounts of histamine. It’s associated with a wide array of symptoms, from flushing and itching to vomiting and diarrhea. 
  • More research is needed to conclude what definitely causes HIT, but research shows that there are internal (genes) and external (diet, medication) related factors 
  • There is a relationship between histamine and the vaginal microbiome, but more research is needed on the exact mechanisms. We know that histamine levels can impact hormone levels and pregnancy. 
  • There is evidence that microbes in the gut microbiome can produce histamine, but more research is needed to see if the vaginal microbes can do the same. 

If you are an AllergyGirl™, you probably have a medicine cabinet full of antihistamines like Benadryl and Zyrtec.  But what exactly is the function of histamine in our bodies? And can it affect the vaginal microbiome? 

We’re digging into the latest research on histamine, where it comes from, what it means to be histamine intolerant, and how all of this can play a role in your vaginal health. 

What is histamine?

Histamine is a naturally occurring molecule that your immune system uses to respond to injuries. 

When we’re injured histamine helps bring in immune cells to the area by causing your blood vessels to dilate, which we experience as redness, swelling, and soreness.

Sometimes, too much histamine can cause an overreaction. If you have seasonal allergies, you know this all too well. That’s why people take “antihistamines” — to dampen an overactive immune response.  

Researchers have found that histamine can do a lot of other things too.

Here’s a quick list of the symptoms histamine is associated with (which is still growing as more research comes out!):

  1. Inflammation: Histamine dilates blood vessels and brings in immune cells to resolve an infection and/or tissue damage. This is why your cuts get red or why you may feel sinus pressure when pollen counts are high. 
  2. Stomach acid secretion: Histamine causes an increase in acid in your stomach, which can cause heartburn and ulcers.
  3. Signaling in the brain: Cells in the brain also produce and respond to histamine. Researchers are actively working to figure out what exactly histamine does in the brain. 

What is histamine intolerance (HIT)?

Histamine intolerance (HIT) is a type of food intolerance that is suspected to be caused by eating foods that have high amounts of histamine, such as certain fish, alcohol, and certain fruits and vegetables

This can cause an over-accumulation of histamine circulating in the blood. Recent studies show which exact foods contain histamine, but the research is far from complete, and there is significant variation between studies.

Researchers believe that multiple factors can contribute to histamine sensitivity

HIT can be difficult to diagnose because not all people experience it the same way, so there are a wide array of symptoms. Some symptoms attributed to HIT include flushing, itching, headache, nausea/vomiting, and diarrhea. 

In a 2019 study of symptoms experienced by people with diagnosed HIT, the most common symptoms were:

How is histamine intolerance (HIT) diagnosed?

In order to diagnose HIT a physician may first rule out other food allergies, and/or wait to see if your symptoms improve upon switching to a low histamine diet or taking antihistamines. We know, not exactly a quick diagnosis! 

What causes HIT, and who gets it? 

The concept of histamine intolerance is relatively new, and is still being investigated. Because of this lack of a definitive mechanism, some physicians and researchers prefer the phrase “adverse reactions to ingested histamine”.

As of right now, no specific mechanism causing histamine intolerance has been demonstrated to reliably cause HIT symptoms in prospective, controlled studies.

From what we do know, HIT is likely caused by a combination of underlying genetic predisposition, diet, the gut microbiome, and certain medications.

These factors can lead to a deficiency in enzymes, like Diamine oxidase (DAO), that degrade histamine

Other than menstrual cramps, no symptoms specific to people with vaginas have been studied or reported. In general, we know that women are more likely to experience food intolerance than men. This could explain why food intolerance is only recently being studied, and why some physicians are initially skeptical about food intolerance symptoms

Gender health gap, we meet again!

Is there a connection between histamine and the vagina?

Short answer? Yes. Research supports a connection between histamine, the menstrual cycle, the vagina, and the vaginal microbiome

However, the research is still very preliminary on how exactly histamine affects the vagina, and how exactly these connections relate to HIT symptoms. 

Here’s what we know so far:  

Histamine and the upper reproductive tract

Most of the research published so far has focused on how circulating histamine influences pregnancy. We know that the uterus contains histamine receptors, which indicates that the uterus can sense and respond to changes in histamine levels. At least two studies so far have found that equilibrium between histamine and the histamine-degrading enzyme Diamine oxidase (DAO) are crucial for a normal pregnancy

Studies haven’t investigated how histamine levels in the uterus affect non-pregnancy health concerns or our overall well being. (Frustrating, since women’s health is so much more than pregnancy-related!) More research is needed to understand how histamine might affect people with uteri throughout other stages of their life.

Histamine, menstruation, and hormones

Researchers have found that levels of DAO in the bloodstream fluctuate throughout the menstrual cycle, with the highest levels at the luteal phase. Since DAO degrades histamine, fluctuating levels could have an impact on how histamine is processed throughout the menstrual cycle. 

We already know that estrogen can influence the vagina and the vaginal microbiome. Researchers found that when ovarian cells are treated with histamine, estradiol (estrogen) levels increase. So it’s possible that histamine’s effect on hormone levels could have a secondary effect on the vaginal microbiome. This is just a theory, there aren’t any studies that have directly tested this yet. 

Histamine and the gut microbiome

The gut contains trillions of bacteria that make up the gut microbiome. It turns out that microbes in the human gut microbiome can produce histamine themselves, and that microbially-produced histamine can cause abdominal pain (at least in mice). Whether or not microbes present in the vagina can make histamine has not been directly assessed though. This is exactly the type of question that data from Evvy’s vaginal microbiome test can help researchers solve! 

Recurrent symptoms? Meet Evvy's at-home vaginal microbiome test, approved by leading OB-GYNs.
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Should I try a low histamine diet and/or take antihistamines?

If you believe that you may have a sensitivity to histamine, speaking to your doctor and/or a nutritionist about your symptoms is a great place to start. They can help rule out other allergies and intolerances first. Speaking with an expert can help you go through the research to help you thoroughly and thoughtfully eliminate foods, and make sure you are still getting all the nutrients needed to thrive. And avoid attempting any intensive elimination diets without consulting a provider or nutritionist first as you can do more harm than good! 

Histamine intolerance is a growing area of research, so the Evvy team will be sure to report back as we learn more about its impact on vaginal health!