Why we get allergies + natural remedies for allergy season

Spring time should be a wonderful time of year, with the weather getting warmer and everything beginning to grow again after the winter, but for those people who suffer from seasonal allergies, the beauty of spring is often blighted with horrible allergic symptoms: a runny nose, sneezing, itchy, watery eyes and an itchy throat as well as blocked sinuses and often changes in mood and sleep patterns. In Europe an estimated 10%-20% of the population suffer from allergies, so is there anything we can do to improve the situation?

Conventional approaches include antihistamine medications and steroids, and while they may sometimes be necessary, my focus as a naturopath is in helping identify and resolve underlying root causes so that the body can respond more appropriately. And as we’ll see, there are many lifestyle and environmental factors that can make these symptoms much worse than they need to be.

The basics of a pollen allergy

When we inhale pollen, immune cells in our respiratory system such as mast cells react by releasing histamine and a host of other immune chemicals. These chemicals act to counter the pollen by stimulating symptoms such as sneezing, mucus production, watery eyes and itchiness which help to remove it from our airways.

This initial reaction also signals to other parts of the immune system to shift our T cells to a th2 dominant response and start producing IgE antibodies from B cells. These antibodies then bind to a receptors on the mast cells sensitising them, so that when we inhale pollen again, our mast cells respond by once again releasing histamine, prostaglandins and other immune chemicals but in a more exaggerated and targeted way¹.

These IgE antibodies are specific to different kinds of pollen, so that is why some people are allergic to certain trees while others are more sensitive to grasses. It’s also the same process for other allergies, such as to cats, foods or medications.

This second response creates immune memory: B cells can last for decades and restart IgE production as soon as the immune system sees the pollen again. The receptor-bound IgE also lasts for several weeks, keeping mast cells sensitised and primed and ready to react whenever we come across more pollen.

Although we associate this mast cell-histamine response with our bad allergy symptoms, this has actually been a lifesaving response throughout evolution that helped us survive all sorts of venoms and toxins in nature, so in the right measure it’s very useful. The problem comes when this response is excessive to relatively harmless things like pollen. While there is still no definitive answer as to why some people react and other don’t, there are some intriguing possibilities and some potential remedies which I’ll get in to shortly – but for now, let’s take a closer look at the allergic response itself.

Histamine & mast cells

Histamine is not just related to allergies and is in fact a very important chemical in the body: it has all sorts of necessary functions – many of which are related to our defence. When our immune system recognises a threat, it responds with many different types of attack, one of them being histamine. Histamine helps us flush away the bad guys: in the respiratory tract it stimulates mucus production and sneezing and in the digestive tract in increases stomach acid, motility and sometimes vomiting – so if we inhale or eat something dangerous for our health, the histamine reaction helps to get it out of the body. It also stimulates inflammation and increased capillary permeability, so if you get a painful, red swelling after an insect bite, this is also a histamine effect, which stimulates inflammation as part of the healing response.

The majority of histamine is released from our mast cells but it is also released from basophils and in small amounts in the brain as a neurotransmitter to stimulate wakefulness. Mast cells are ‘first responder’ immune cells that represent a first line of defence – they are found in areas of the body that are more exposed to the outside world with most being located in the respiratory tract, the digestive tract, the skin and eyes. When they sense a threat, they are able to quickly release histamine, prostaglandins, cytokines and other chemicals in a fraction of a second through a process called degranulation.

In people who suffer from seasonal allergies, these mast cells increase in number and become sensitised and more reactive to different types of pollen, which generates higher levels of histamine. Histamine issues are not just about allergies however, and conditions such as MCAS, mastocytosis and histamine intollerance are gaining notoriety, and may also be an important factor a host of other issues including IBD, gastritis, bladder pain, asthma, cardiovascular problems, skin issues, insomnia and problems with balance.

Why doesn’t everyone react to pollen?

For many people, pollen isn’t a problem. Exposure creates mild symptoms if any, and repeated exposure creates immune tolerance. With immune tolerance, the immune system learns to ignore the pollen, just like it does with food (most of the time). This means our IgE antibodies switch to IgG4, and T regulatory cells produce molecules like il-10 and TGF-beta which help calm inflammation and reduce mast cell activity².

But for those that suffer from allergies, this doesn’t happen: memory B cells keep producing the IgE antibodies and mast cells keep reacting, so every time pollen season comes along, so do our symptoms.

To understand this, we need to consider one of the main jobs of the immune system: to decide what is harmful and what is not. We need to eat and breathe to stay alive, but with eating and breathing comes the risk of taking in something harmful which the immune system needs to deal with. Generally speaking, the immune system does this job amazingly well, but in the case of seasonal allergies, mast cells can end up overreacting. 

But why? While there isn’t a definitive answer to this, there are some intriguing ideas. When looking for a cause behind something, we can consider nature and nurture – or in other words genetic tendencies and environmental factors including the influence on how genes are expressed.

With allergies, there are some important genetic considerations, and children often have the same allergies as parents – but while we can’t do much about our genetics, environmental and lifestyle factors are often modifiable, and as it turns out with allergies these may also play an important role..

….the way we eat, lack of exercise and sunshine, our microbiome, our stress levels, childhood trauma and exposure to certain elements such as heavy metals, synthetic chemicals such as pesticides and air pollution all have the ability to push the immune system into a more allergic state which is both more reactive to pollen and less able to generate immune tolerance.

Imagine someone has an argument with a spouse before leaving for work. It could be that while walking to the bus stop, the people we encounter who’ve done nothing wrong seem annoying and antagonistic. And in this analogy, it is these innocent bystanders that represent pollen. Our immune system reacts against the pollen not because it is dangerous, but because the immune system is in a hyper-reactive state.

The allergy-primed state

The allergy-primed state is how I describe this state where the body is already under stress, and when pollen comes along – we get both an over reaction and an inabilit to generate immune tolerance. This translates to persistently high IgE levels and allergic symptoms. Key characteristics of this state are an immune response with a dominant th2 reaction, weaker T regulatory activity and xenobiotic/stress sensitisation of mast cells. But what does that mean?

Our immune system is divided into different branches that deal with different things. One branch is our T helper cells which are part of the adaptive immune system. Our T helper 1 (th1) response that deals with killing intracellular viruses and bacteria, while our T helper 2 (th2) response deals with anything outside of the cell such as parasites, some bacteria, toxins and allergens like pollen. A common idea is that Th1 and Th2 balance each other, so that if Th1 is stronger, Th2 would be weaker and vice versa, and while this model has been somewhat superseded with the discovery of Th17 and other advances, it is still a relevant way of looking at it because the immune system has limited resources which it needs to invest wisely. If you live in a place with lots of bacteria, the immune system needs to get good at killing bacteria, whereas if there are more parasites for example, then that is what needs attention.

Having a dominant Th2 response makes us more sensitive to allergens such as pollen and more prone to allergic reactions and asthma because it increases mast cell numbers and reactivity via increased immune chemicals such as interleukins 4, 5 and 13. Il-4 and il-13 have been extensively studied for their effect on allergies and are key players in the propagation of the allergic response³. For example, il-4 has been shown to increase the number and reactivity of mast cells which increases histamine, mucus production and other allergy symptoms. It also increases the expression of the FcεRI receptor on mast cells⁴. Il-4 goes on to stimulate IgE antibody production from B cells, and il-4 is also produced by mast cells which increases Th2 cells^{5 6}.

Some things that might induce th2 dominance from human and animal studies include:

• Heavy metals such as mercury^{7 8} and aluminium⁹
• Air pollution^[10][11]
• Gut dysbiosis
• Chronic psychological stress^12[13][14]
• Trauma¹⁵
• Magnesium deficiency¹⁶
• BPA¹⁷
• Mould toxins¹⁸
• Fungicides such as Azoxystrobin and Iprodione¹⁹
• Histamine²⁰

So if someone is exposed to anything on the list above such as city smog or micotoxins from the diet, it could mean that the same amount of pollen that never used to cause any issues has us now sneezing, itchy and reaching for the tissues.

T regulatory cell dysfunction

The T regulatory cells are another category of our T helper cells, and their job is to calm things down. They produce anti-inflammatory chemicals such as il-10 and TGF-beta which reduce the activity of other immune cells including th2 and mast cells so that we don’t overreact to things. They are also involved in the switch between IgE and IgG4 antibodies which creates immune tolerance²¹, and when doctors do blood tests for food allergies, they are looking for high IgE antibodies to certain foods because that suggests a lack of immune tolerance and possible reactions against them.

As well as suppressing the th2 response, T regulatory cells are also important in protecting the nasal mucosa barrier and helping to return this epithelial layer back to normal after an allergic episode, as well as reducing mucus production.

Some studies have set out to test the blood of both allergy sufferers and healthy controls finding that the allergy sufferers have lower levels of T regulatory cells and higher IgE levels²². Although other studies have produced mixed results and more research is needed, it certainly seems like T regulatory cells play an important role in minimising allergic symptoms, a conclusion that has been further backed up by animal models of allergic rhinitis which shown benefit from interventions which boost T reg cells²³.

T regulatory cells are strongly impacted by environmental factors. A lack of exercise and vitamin D from sunshine and fibre in the diet are three important causes of low T reg cells, as well as intestinal dysbiosis and exposure to many elements of modern life, including refined foods, alcohol, microplastics, BPA and many others. The general health of the intestine has a big impact on T regulatory numbers, and mice raised in sterile conditions also had low T reg numbers which were restored with the introduction of certain probiotics. Fibre is an important dietary component because it gets metabolised by our gut bacteria into short chain fatty acids like butyrate which have been shown to increase T regulatory numbers. Vitamin A, zinc, selenium and unsaturated fatty acids have also been shown to be important in this regard^{24 25}.

Xenobiotic sensitisation of mast cells

An interesting 2021 study²⁶ found evidence that synthetic chemicals could disrupt mast cells rendering them more likely to react to future exposures. The authors called it TILT, or ‘toxicant induced loss of tolerance’ and suggested this could explain chemical intolerance – a condition that makes people hypersensitive to synthetic chemicals. The key is a two step process where previous exposure reduces tolerance to future exposure, and although the authors didn’t go on to look at seasonal allergies in this paper, it seems like it would be likely that anything capable of stimulating an IgE/mast cell response could potentially act as a trigger.

Key xenobiotics include agrochemicals such as pesticides, insecticides and fungicides, products of industry such as bisphenols and dioxins, household items like cleaning products and air fresheners, new car smell, food additives, smoke and so on.

It will be interesting to see where this goes in the future, but in the meantime trying to limit exposure to these types of chemicals has numerous, well studied health benefits.

Stress, trauma & the allergy-primed state

It has long been recognised that stress can make existing allergies worse, but could stress also contribute to the creation of new allergies? Anecdotally, some say that childhood allergies often appear in times of stress and trauma, but is there any evidence for this? A large 2022 study published in the American Journal of Epidemiology²⁷ suggests that there could be a link between transgenerational and childhood trauma and an increased risk of allergies. They posit that HPA axis dysregulation following early life stress may reduce cortisol levels which leads to th2 dominance and increased allergies and asthma. Acute stress is well known to increase cortisol, but chronic stress seems to decrease it adaptively. This is also seen in Chronic Fatigue Syndrome which typically demonstrates blunted cortisol levels²⁸ although some studies have also shown th2 dominance with increased cortisol²⁹. This is interesting, because histamine issues have long been linked with CFS. And increased asthma levels have been noted in dealing with grief³⁰, which could also be related to a th2 shift.

Another interesting study carried out skin prick tests on volunteers before and after they underwent a stressful event in the lab and found that the anxiety made them significantly more reactive, even when the test was performed the following day³¹. It was noted that a significantly smaller dose was required to elicit the same response.

Stress has also been found to impact T regulatory cells, with increased cortisol being linked to lower T regulatory cell numbers ³². The finding in this study was related to ER stress in the T regulatory cells.

With an increased th2 response and reduced T regulatory cells, pollen is more likely to create high levels of mast cell activation, histamine and IgE production and memory in B cells.

Impaired histamine breakdown

If histamine symptoms are more systemic there may also be an issue breaking histamine down. Just like everything else in the body, histamine has to be broken down after it’s been used, and there are two main enzymes that do this job. Both genetic and environmental factors can impair these enzymes, meaning that histamine levels and symptoms can increase. Extracellular histamine is broken down by DAO, which is expressed mostly in the digestive tract and intracellular histamine is broken down by HNMT, expressed at highest levels in the brain, liver, kidney, thyroid, brochus, skin and also the digestive tract³³.

Good nutrition is key to this process. DAO requires vitamin C, copper, B6, B12, iron, magnesium and zinc to function correctly and can be inhibited by many things including alcohol and estrogen. HNMT is a methy tranferase enzyme so it requires good methylation status in order to disactivate histamine effectively. The main methy donor in the body is SAMe which is made from methionine, and key nutrients in this process include folate, B2, B6. B12, choline and betaine³⁴.

Lifestyle changes for allergies

Let’s now take a look at some lifestyle changes and natural remedies that can help support the body during allergy season.

#1 Reduce exposure

Reducing exposure to pollen is easier said than done during allergy season because it gets everywhere, but one change that can really make a difference is keeping the bedroom as free from pollen as possible so that we can get a good night’s sleep. This includes regularly dusting and hoovering the bedroom, regularly changing the bed sheets, having a shower before bed and keeping pets out of the bedroom or at least off the bed as dogs and cats tend to bring pollen with them. A silent HEPA air filter can also be a good addition to improve the air quality.

#2 Lower stress

As we have seen, stress can exasperate histamine issues. It does this in part because cortisol affects th2 expression, but also because CRF (our primary stress hormone) can stimulate mast cells to release histamine, so where possible we should reduce the level of stress. It’s not always easy to reduce stress as modern life is often stressful by default, but some great things to focus on include getting to bed early, physical exercise, socialising with friends and mindfulness and medication techniques. It might also be a time to start addressing deeper psycho-emotional trauma and dysfunctional relationships as these can also be considerable sources of stress. Some people find that their allergies started at a particularly stressful moment in their lives, so this should not be ignored and instead worked through where possible.

#3 Love your liver

The liver is the main site of histamine breakdown, and in the springtime it can often get overburdened if the liver is weak in general. Common signs may include difficulty going to the bathroom including sticky poops, dizziness and a bitter taste in the mouth. In Traditional Chinese Medicine, the liver and gallbladder are the primary organs associated with the wood element, and spring is the time when this element is most active. This means that if there is any imbalance in this system, we are more likely to see it during the springtime, which according to TCM can appear as headaches, feeling irritable or frustrated – so springtime is the ideal season to support the liver. From a Western point of view, reducing the intake of heavy foods and alcohol and reducing toxic exposure are key steps, together with foods and herbs that support phase I and phase II detoxification including adequate, high quality protein and plenty of green vegetables.

#4 Dietary changes

During allergy season, high histamine foods can be an extra burden on the bodily systems that break down histamine. especially if you notice more systemic histamine symptoms such as itchy skin, gastrointestinal problems and sleep issues. These foods include all fermented foods including alcohol, rice vinegar, cheeses and seasoned meats as well as most types of fish, especially canned fish and shellfish³⁵. Fish that is very fresh or that has been flash frozen immediately after being caught don’t usually present a problem. Citrus fruits, chocolate, tomatoes and legumes have also been found to stimulate the release of histamine. If you only have symptoms in the respiratory tract this may apply less to you as this applies more to systemic histamine issues like MCAS, but many allergy sufferers also have some degree of systemic histamine intolerance. so be aware of any reactions.

Another change that often benefits allergy sufferers is to cut out dairy. Dairy is mucus forming and can make allergies much worse in some people.

Finally, Ensuring a nutrient rich diet will benefit allergy sufferers in many ways. Not only in providing nutrients like vitamin C which help reduce histamine load, but also the nutrients mentioned above that help to break down histamine. A nutrient rich, fibre rich, unprocessed diet also helps to improve microbiome health, another important aspect of immune balance.

#5 Reduce your toxic burden

Previously I mentioned two ways in which toxic elements can make allergies worse: firstly by directly interfering with mast cells to make them more reactive, and secondly by shifting the immune system towards a Th2 dominant state which amplifies allergic symptoms. While going into detail about every possible toxic element is beyond the scope of this article, there are some general principles to follow: try reducing everyday exposure to pesticides and other agrochemicals by eating a clean diet, and avoiding non-organic foods from the dirty dozen list³⁶. This is a list compiled by the EWG in the US of the most heavily contaminated foods, and includes strawberries, spinach, kale and other greens, grapes, peaches, pears, apples, cherries, blueberries and green beans. Use personal care products sparingly and always opt for more natural brands. For example, make-up can be loaded with heavy metals such as lead and deodorants with aluminium should be avoided. With regards to animal products, fish with high levels of mercury like sword fish and tuna should be avoided as well as farmed fish and intensively raised livestock where possible, and a diet rich in fibre and phytochemicals can help the body remove some of the toxic burden. Lastly, high quality, clean protein is important in order to support glutathione levels which are essential in dealing with and removing all sorts of toxic elements from the body.

#6 Get more sun and exercise

As mentioned, both vitamin D and exercise increase T reg cells which help to reduce th2 dominance and improve immune tolerance, but they both have many other benefits for our health. Beyond vitamin D, sunshine increases nitric oxide which has been found to reduce the IgE-mediated mast cell activation³⁷. Even though some studies have found an increased th2 response, IgE antibodies have been found to be lower, probably due to a significant increase in il-10³⁸. Vitamin D supplementation has also been found to reduce allergic symptoms³⁹, although it is preferable to get vitamin D from sunlight exposure.

Natural remedies for allergies

#1 Vitamin C

If you’re trying to reduce allergy symptoms, vitamin C should be an essential part of your plan. A 2023 review⁴⁰ found vitamin C to be helpful in reducing allergy symptoms and several studies have found higher doses to be correlated with lower blood histamine levels⁴¹⁴². Firstly, it helps to stabilise mast cells especially with adequate B6⁴³. It also decrease histamine production by inhibiting the histidine decarboxylase enzyme⁴⁴. And, it helps in the breakdown of histamine being an essential cofactor in the DAO enzyme⁴⁵. Doses for histamine reduction range from 250mg to 750mg a day, although larger doses of 2-3 grams have been used successfully short term. Longer term intake of higher doses may lead to oxalate and kidney stone issues. The best forms to use are natural extracts such as acerola as they also contain bioflavanoids, but high quality buffered forms such as sodium ascorbate can also work well.

#2 Nigella sativa

The seeds of Black cumin, or Nigella sativa, are used in North Africa and Middle Eastern cuisine, and have a wide range of health benefits. Although studies are preliminary, it seems the seed oil has important anti-allergic and anti-inflammatory effects. One small RCT found significantly less allergic symptoms⁴⁶ and a recent review found benefits for respiratory, allergic and immunologic disorders⁴⁷. One in vitro study suggested this could be due to reducing histamine release from mast cells⁴⁸ while others have suggested immunomodulatory effects in reducing il-4 and increasing IFN⁴⁹ without affecting th1/th2 cell numbers, although not all studies agree^{50 51 52}.

#3 Spirulina

Spirulina is a blue-green algae that is actually a bacteria. It is full of nutrients and may also hold promise for allergies. A 2020 randomised controlled trial found that 2g of spirulina per day was significantly more effective than 10mg cetirizine for allergic symptom reduction⁵³. There were also significant changes in cytokine levels, with the treatment group having lower il-1α, il-1β and il-4 and higher il-10.

If you’re thinking of trying spirulina though, make sure you find a quality brand. When grown in poor conditions, spirulina can be contaminated with heavy metals, pesticides and other types of algae – some of which are toxic to the liver. Always go for a trustworthy organic brand that is lab tested. Although spirulina is anti-allergic for most, there have been a handful of cases of spirulina allergy, so as with all new supplements, start out with a small dose or avoid if allergy is suspected.

#4 Flavanoids

Flavanoids are plant chemicals often associated with health benefits, and some of the most researched for allergies include Quercetin, Kaemferol, Myricetin and Luteolin. They are anti-inflammatory and may help to regulate th1/th2 balance as well as having been found to stabilise mast cells and basophils and decrease their histamine release⁵⁴.

Foods rich in quercetin include capers, red onions, apples, cranberries dill and nettle.

Foods rich in Luteolin include radicchio, green peppers, artichoke, thyme and Mexican oregano.

#5 Perilla

Perilla frutescens is a sweet, culinary used across Asia as well as in TCM. Its benefits for allergy relief stem from the rosmarinic acid and luteolin content, and in one small randomised controlled trial it showed significant symptom reduction and a reduction in eosinophils and neutrophils in nasal fluid⁵⁵. A similar study by some of the same authors on rosmarinic acid also yielded positive results⁵⁶. Animal studies suggest it can also reduce inflammatory markers such as il-1b, TNF-a, caspase-1 and cox-2⁵⁷.

#6 Astragalus

Astragalus is a herb used in TCM and has been extensively studied for its effects on the immune system. In a small randomised controlled trial an astragalus root product showed some significant benefits for allergy suffers⁵⁸. This might be because of its beneficial effect on reducing th2 and increasing T regulatory cells⁵⁹, or because it contains flavanoids linked with mast cell stabilisation⁶⁰.

Because of its immune modulating properties, astragalus should only be used under medical supervision in cases of autoimmunity and should be avoided in cases of organ transplant.

#6 Gynostemma

Gynostemma pentaphyllum, also known as jiaogulan, is a herb that is used in Asia and drunk like green tea in South Western China, although it is not used commonly in TCM which developed more in Central China. It is an adaptogenic herb with some exciting potential benefots although research is at an early stage and there is a lack of human studies. In animal models it has been found to significantly reduce th2 cytokines and increase th1 activity⁶¹.

References:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3581154/ ↩︎
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3885784/ ↩︎
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4532630/ ↩︎
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4532630/ ↩︎
5. https://pubmed.ncbi.nlm.nih.gov/15905515/ ↩︎
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9161813/ ↩︎
7. https://jlb.onlinelibrary.wiley.com/doi/full/10.1189/jlb.0706467 ↩︎
8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10794242/ ↩︎
9. https://pubmed.ncbi.nlm.nih.gov/10586035/ ↩︎
10. https://journals.aai.org/jimmunol/article/172/6/3808/36172/Diesel-Exhaust-Particles-Suppress-In-Vivo-IFN ↩︎
11. https://pubmed.ncbi.nlm.nih.gov/23121301/ ↩︎
12. https://www.sciencedirect.com/science/article/abs/pii/S0074774202520092 ↩︎
13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5688230/ ↩︎
14. https://www.tandfonline.com/doi/abs/10.1080/08964280009595761 ↩︎
15. https://academic.oup.com/aje/article/191/1/38/6373815 ↩︎
16. https://pubmed.ncbi.nlm.nih.gov/20546583/ ↩︎
17. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4002911/ ↩︎
18. https://pubmed.ncbi.nlm.nih.gov/20194814/ ↩︎
19. https://pubmed.ncbi.nlm.nih.gov/33226166/ ↩︎
20. https://pubmed.ncbi.nlm.nih.gov/12810348/ ↩︎
21. https://onlinelibrary.wiley.com/doi/10.1111/j.1398-9995.2008.01774.x ↩︎
22. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6881876/ ↩︎
23. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8563054/ ↩︎
24. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9205643/ ↩︎
25. https://www.frontiersin.org/articles/10.3389/fnut.2022.878382/full ↩︎
26. https://link.springer.com/epdf/10.1186/s12302-021-00570-3 ↩︎
27. https://academic.oup.com/aje/article/191/1/38/6373815 ↩︎
28. https://www.ncbi.nlm.nih.gov/books/NBK279099/ ↩︎
29. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3018761/ ↩︎
30. https://www.sciencedirect.com/science/article/pii/S0033318285727594 ↩︎
31. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819057 ↩︎
32. https://onlinelibrary.wiley.com/doi/10.1111/imm.13669 ↩︎
33. https://www.proteinatlas.org/ENSG00000150540-HNMT/tissue ↩︎
34. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4004707/ ↩︎
35. https://www.histamineintolerance.org.uk/about/the-food-diary/the-food-list/ ↩︎
36. https://www.ewg.org/foodnews/dirty-dozen.php ↩︎
37. https://www.scielo.br/j/mioc/a/tDMCGPMdk3CHhzJfHcy3GRB ↩︎
38. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2326852/ ↩︎
39. https://link.springer.com/article/10.1007/s12070-021-03004-x ↩︎
40. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9970132/ ↩︎
41. https://pubmed.ncbi.nlm.nih.gov/1578094/ ↩︎
42. https://pubmed.ncbi.nlm.nih.gov/8951736/ ↩︎
43. https://www.cellphysiolbiochem.com/Articles/000534/ ↩︎
44. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4903110/ ↩︎
45. https://pubmed.ncbi.nlm.nih.gov/25095772/ ↩︎
46. https://pubmed.ncbi.nlm.nih.gov/20947211/ ↩︎
47. https://onlinelibrary.wiley.com/doi/10.1002/ptr.7003 ↩︎
48. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6194640/ ↩︎
49. https://paediatricaindonesiana.org/index.php/paediatrica-indonesiana/article/view/1399 ↩︎
50. https://pubmed.ncbi.nlm.nih.gov/20600757/ ↩︎
51. https://pubmed.ncbi.nlm.nih.gov/16125022/ ↩︎
52. https://www.mdpi.com/2076-3921/12/6/1246 ↩︎
53. https://pubmed.ncbi.nlm.nih.gov/32773785/ ↩︎
54. https://www.sciencedirect.com/science/article/pii/S0753332222013348 ↩︎
55. https://journals.sagepub.com/doi/10.1177/153537020422900305 ↩︎
56. https://pubmed.ncbi.nlm.nih.gov/15630183/ ↩︎
57. https://pubmed.ncbi.nlm.nih.gov/21239739/ ↩︎
58. https://onlinelibrary.wiley.com/doi/10.1002/ptr.2877 ↩︎
59. https://jissn.biomedcentral.com/articles/10.1186/s12970-021-00425-5 ↩︎
60. https://pubmed.ncbi.nlm.nih.gov/18958421/ ↩︎
61. https://www.mdpi.com/1422-0067/23/14/7699 ↩︎