• -Natalie

What Causes Food Allergy?

Ever heard of the five Ds? They stand for dry skin, diet, vitamin D, dirt, and dogs. And they are the five biggest players when it comes to the development of IgE-mediated anaphylactic food allergies. But they probably don't actually mean what you think they do, so make sure to keep reading.

Dry Skin

Infants with early-onset and more severe eczema are more likely to develop food allergies. Ever thought about why?

Eczema is an allergic disease, and so are food allergies. So if you already have one allergic disease. you are probably at a higher risk of developing another one, right?

While this is true, this is not the main reason that infants with eczema go on to develop food allergies specifically.

Cutaneous exposure to antigens can lead to sensitization. That means that developing an allergic response to food can occur by exposure to the allergen through the skin.

The skin contains lymph nodes (white blood cells) that can initiate a Th2 memory response leading to allergic sensitization - or what we refer to as allergy. (Read more about Th2 below).


Early introduction involves introducing an infant to allergenic foods such as peanuts and milk at an early age in order to try to prevent the development of food allergies. But what is it specifically about introducing infants to these foods?

As mentioned above, if food is exposed to the infant through the skin, it can lead to sensitization. But it has been found that if an infant is exposed to food via the oral route, it can actually lead to oral tolerance.

Vitamin D

This vitamin is a fat-soluble vitamin present in few foods. The main role of vitamin D is the absorption of calcium, which is why it is typically related to bones.

But this vitamin is widely underrated. It also plays important roles in the reduction of inflammation and immune function. Various studies have found that infants with vitamin D insufficiency (<50nmol/L) are more likely to have food allergy.


I promise that if your infant goes outside and eats a handful of dirt, they will not be reducing their chance of developing food allergy. In fact, they will be significantly increasing their chances of contracting E.Coli or Salmonella. This is especially dangerous for infants whose immune system is still developing and may not be able to properly fight off these bacterial infections.

By dirt, we actually mean the microbiome. Our gut is made up of millions of bacteria that help our immune system function properly. If the microbiome composition is thrown off, this can lead to a dominant Th2 response, which can then lead to allergic diseases, including food allergy.

There are various studies (I have written summaries here on my blog about some of them) that show certain strains of bacteria are linked to a dominant Th2 response. Thus, it is important to maintain a "healthy" microbiome. Why is "healthy" in quotation marks? Because we still don't actually know what constitutes as a healthy microbiome, meaning we don't know which bacteria and in what amounts are optimal.

We do know of ways to try to maintain a healthy microbiome though. This includes breastfeeding if possible, not delaying introduction to solids (but also not introducing them too early), and eating a diverse diet.


What do dogs have to do with this?! Don't worry, they actually play a positive role! (Could dogs get any better?)

Not only is our internal microbiome important (which is achieved through ingesting food), but our external microbial exposure is equally important!

And dirt is not the answer, but dogs are. It has been shown that infants with pet dogs and older siblings are less likely to have food allergy - both of which contribute to the external microbiome.

So What's The Takeaway?

If you buy a dog right now, I can absolutely guarantee that you are going to receive so much unconditional love and they will become your new best friend, but it does not automatically mean that your infant will not develop food allergies.

So what's the point of all of these separate hypotheses/correlations if none of them can actually guarantee the prevention of the development of food allergies?

Well, think of it this way. The sun can cause skin cancer. Does that mean that everyone who exposes themselves to the sun will develop skin cancer? Absolutely not. Does that mean that some people who expose themselves to the sun will develop skin cancer? Yes. Does it mean if someone wears sunscreen they are completely 100% protected against skin cancer? Obviously not. But does it reduce the chance? YES!

So it's kind of the same thing. If you put all of these together, you may be able to reduce the CHANCE that your infant will develop food allergies.

It‘s specifically our Th2 component of our immune system which is responsible for driving allergic disease. A healthy immune system expresses the Th2 component but in a regulated manner. In allergic disease, the Th2 component is not suppressed and is rather over expressed. All of the factors listed above play a role in the immune system not functioning properly by throwing off this Th2 balance and regulation.

Info taken from the American College of Allergy, Asthma, and Immunology conference 2020.

Additionally, https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

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