Why Are Some People Allergic to Certain Foods?

Why Are Some People Allergic to Certain Foods?

Where is the tightest security control in the world? In the banks? Or at Airports? One of the strongest security controls in the world is inside us. Yes, indeed, our immune system is one of the strongest defense systems in the world.

So why does this strong immune system also react to harmless foods? For example, when most people eat peanut butter, their bodies start to react as if they have been poisoned. But how does this harmless peanut butter confuse this powerful defense system? Or is this security not as perfect as we thought?

What Does Our Immune System Do When We Eat?

We can imagine our immune system like this: When we eat something, for example, a non-allergenic food such as chicken, the proteins of that food pass through the safety check. Cells that provide this security control are also called IgE cells. Only if these IgE cells give approval, the food can enter.

For example, when we eat chicken, the security personnel say, ‘Yes, it’s just chicken. It is not dangerous and cannot harm us. You can pass‘. There is no problem here.

Food Allergy

But let’s say you’re allergic to peanut butter and you ate peanut butter. This time, the IgE antibodies are almost baffled. No, it can’t be. It looks like a parasite. This could be dangerous for me.” They do not allow the passage, saying, “I must kill it immediately”. They then call support by pressing the emergency button.

The incoming immune system’s dedicated officials are trying to destroy the proteins of peanut butter. These police chiefs resort to the most effective weapon they have: Histamine.

Histamine is such a reckless chemical that it is ready to do anything to kill its target molecule. It may even risk killing you to protect you!

Food allergy

Allergy Medications: Antihistamines

This sweet conservative chemical is actually the cause of allergy symptoms in our bodies. The swelling, redness, and itching of your body, which is one of the allergy symptoms, is all because of this overprotective friend. That’s why when you show allergy symptoms, you drink allergy medications that have an antihistamine written on them.

allergy medicine

Yes, we learned how our body’s defense system basically works. So how come the difference between peanut butter and parasite is indistinguishable?

Protein Similarities

Wanting to answer this question, a biologist, Nidhi Tyagi, observes metazoan parasites and peanut proteins. As a result of his study, he concludes that the similarity between peanut protein and parasite protein is 63%. That’s a pretty high number. We can interpret this high similarity rate as follows: Parasite protein and peanut protein are so similar in shape that our immune system cannot distinguish the difference. That’s why it thinks the harmless peanut is a dangerous parasite.

Okay, the similarity to protein might be a reason, but then why are only some people allergic to peanut butter? If the only problem is protein similarity, shouldn’t everyone be allergic?

To answer this question, we must look to the second reason: the Hygiene Hypothesis.

Hygiene Hypothesis

In the past years, the decision of many doctors was this: Children should be raised in healthy environments away from bacteria. In addition, foods that are at risk of allergens should not be consumed until a certain age. These words, which are said as a precaution, seem quite right at first glance, but this method does not reduce the rate of food allergy. On the contrary, it is accelerating.

According to the Fair Health Organization report, the rate of food allergies resulting in serious problems has increased by 377%. Scientists who wanted to find out the reason for this extraordinary increase that took place from 2007-2016 began to suspect hygiene. And then they looked at this map.

Asthma prevalence in the world

This map published by Global Burden of Disease shows the intensity of asthma disease in 2017 by country. When we look at developed countries such as Denmark, Australia, or Northern European countries on this map, we see that asthma is more common in red. But African countries or less developed countries such as India are light yellow, meaning asthma is not common in these countries. This distribution in asthma also questioned the causes of food allergies. As a result of these studies, scientists began to ask the following question: Are we too clean?

Are we too clean?

Yes, the hygiene hypothesis says just that. We are raised in very hygienic environments. Therefore, our immune system cannot meet enough microbes or allergens and cannot complete its development. Our immune system, which is not strong enough, cannot tell the difference between parasite protein and peanut protein.

In fact, the idea behind the hygiene hypothesis and vaccines are similar in one respect. Intake of small amounts of harmful microorganisms in vaccines also strengthens our defense system. The hygiene hypothesis also argues that those who grew up in a dirtier environment as children would have a stronger defense system. Sounds logical, doesn’t it?

But we must not forget that this is just a hypothesis. Although there are various studies, it is not possible to conclude a definite result yet. There is also a variety of data supporting the counter-arguments. Therefore, your doctor will always give you the most accurate information about when children should start to eat allergenic foods.

Unfortunately, we have not yet found a cure for allergies. However, when we examine the history of science, we observe that many ideas that we called mysteries in the past are now becoming reality. Of course, one day, science will find a cure for allergies. We have to believe and trust it. May your faith in science never end.

References and Further Readings

Asthma prevalence. (n.d.). Retrieved from

Bloomfield, S. F., Stanwell-Smith, R., Crevel, R. W., & Pickup, J. (2006). Too clean, or not too clean: the hygiene hypothesis and home hygiene. Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology, 36(4), 402–425.

Food Allergy in the United States: Recent Trends and Costs. (2017). Retrieved from

Tyagi, Nidhi, et al. “Comparisons of allergenic and metazoan parasite proteins: allergy the price of immunity.” PLoS computational biology 11.10 (2015): e1004546.

You can access the sources of the images used by clicking on the images.

The proofreading has been done by Asu Pelin Akköse and Mete Esencan.

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Mete Esencan

Hello everyone! I'm Mete Esencan. I am a graduate student in the Department of Chemistry at METU. I was planning to establish a platform by combining the research knowledge I gained during my basic science education and the management experience I gained in the METU Chemistry Society, which I was in charge of for three years. For this purpose, in February of 2021, I took the first step and established the OkButWhy, a platform where we can write articles as if to chat about science, art and philosophy. I wish everyone a pleasant reading!

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