There’s more to learn about protecting your baby from peanut allergies. Read our Peanut Allergy Guide to discover how you can lower your child’s risk of developing a peanut allergy.

What Causes Peanut Allergies?

Peanut allergies are caused by the body’s overreaction to an otherwise harmless protein. The cause is a combination of genetics, stomach and skin health, and environment. But the exact combination is still unclear. 

Having a parent or sibling with a peanut allergy increases your baby’s risk of developing a peanut allergy, but vulnerable skin (often caused by eczema) and avoidance of the allergen have a bigger effect.  

Immune antibodies chasing a peanut

With a peanut allergy, the immune system mistakes peanut protein for a harmful substance, creates antibodies specific to peanut, and then attacks the peanut. 

Your body attacking the peanut protein is what you see as the allergic response. Your body does a few things to get rid of the peanut and keep more from getting in, like producing hives, inducing vomiting or diarrhea, slowing the blood flow, and closing the airways.

It can be helpful to think of the immune system like the military that protects a country. The soldiers react to ships that show up where they shouldn’t be and marks them as an enemy. On the other hand, soldiers ignore planes and ships that bare their own flag, and use the right call signs.

If peanut were actually dangerous, an attack response would make a lot of sense. But with a peanut allergy, the body is attacking for no reason. 

In a peanut allergy, your baby’s immune soldiers decided that peanut was dangerous even though it isn’t, because peanut protein showed up someplace it shouldn’t. 

After a lot of research, we know that eczema, gut health, and environment are important factors in causing a peanut allergy, because they all allow peanut to show up where it shouldn’t.

Dancing peanuts 


Eczema leaves breaks in your baby’s skin. These breaks may be worse if your baby’s skin is always dry and missing a protein — filaggrin — that makes the skin soft and springy. Without filaggrin, the skin gets rough and broken. 

These breaks could also be caused by having the wrong bacteria (microbiome) living on your baby’s skin. Good bacteria help protect the skin, but the wrong bacteria can allow it to dry out.

When the skin is broken, little bits of things in the outside world can sneak through. And this is where the environment comes in. 


Just like your cat sheds and your shoes bring in dirt, when you eat, you leave little teeny bits of food everywhere. Americans love peanuts, and eat about 7 pounds of them per person every year. Every bite of peanut lets a little bit of peanut into the air, and eventually onto clothes, rugs, floors, and beds. 

If you eat peanuts in your house, your baby is being exposed to peanuts on his skin, no matter how often you vacuum. And if your baby has eczema, that peanut might get into the cracks in his skin...and get through. 

On the other hand, babies in countries where peanuts are not part of the food (like Ireland), rarely develop peanut allergies because they are not getting exposure to peanuts. 

Studies in mice have shown that if peanut goes through cuts in their skin, their immune system goes on high alert. And if they scratch those cuts, their immune system really revs up. 

This is what happens to babies with eczema. When peanut gets through the skin, babies’ immune systems go on alert about peanuts, and “learn” that peanuts are a strange, potentially dangerous thing. 

Stomach Health

The same thing also happens to babies with the wrong microbiome, or bacteria, in their stomachs and intestines. Having the wrong bacteria is called dysbiosis. And in dysbiosis, instead of thickening your baby’s stomach lining, the bacteria leave it weak or make it inflamed.

A weak intestinal lining can cause leaky gut, which is exactly what it sounds like. In leaky gut, some food proteins can leak through the gut, and your baby’s immune system reacts like any soldier might to someone found where they are not supposed to be.  

Understanding food allergies as a response to an unknown threat also helps explain why feeding babies peanuts as a regular part of their diet can prevent peanut allergies. Studies have shown that feeding babies peanuts teaches them to tolerate peanut. Their immune system learns peanuts are okay and lets them pass on by.

Once your baby’s body learns that peanuts are safe, even if the peanut protein breaks through the skin or leaks through the gut, the body’s immune system stays calm. 

Dancing peanuts

So What About Genetics?

Genetics play some role, but peanut allergies are mostly not genetic. As we mentioned above, babies are more likely to develop food allergies if they have parents with eczema, asthma, or food allergies. But skin and gut health, and the environment they grow up in have a greater effect on a baby’s risk of developing a peanut allergy.

For babies, having a parent with:

  • Asthma or eczema doubles the rate of food allergy. 
  • Seasonal allergies nearly doubles the rate of food allergy.
  • A food allergy increases the risk of developing a food allergy almost 6x.
  • Two or three allergic conditions (asthma, eczema, food allergy, seasonal allergies) also doubles or triples the rate of food allergy. 

There are some gene clusters that are linked to the chance of developing a food allergy. But before you run off and get a genetic test from 23andme for a peanut allergy, you should know there is no one peanut allergy gene. 

Even if you checked for a set of genes, it wouldn’t prove that your baby was going to have a peanut allergy. Genes don’t work by themselves. 

Some people have genes to be tall. But if they don’t get enough food when they are little, they might end up short. Genes increase the chance of something, but they don’t guarantee it. 

Now the doubling or tripling of your baby’s risk for developing peanut allergies may sound like a lot, but it only takes the risk from 10% to 20%. Children with no family history, or no peanut allergy gene still have a 10% chance of food allergy. 

Another way we know that the story is bigger than genetics is that even in identical twins, one baby can develop food allergies while the other baby is fine, or have a different reaction. 

Identical twins share the same exact genes, and they often grow up to look similar, but you can tell them apart. In that same way, genetics is just one piece of the peanut allergy puzzle. 

Dancing peanuts

How Are Peanut Allergies Different From Other Allergies? 

They’re not, really. All allergies are basically the same. 

An allergy is when the immune system reacts to something it shouldn’t. Peanuts are just one thing the immune system reacts to. Others are eggs, bananas, pollen, latex, medicines, even water. 

Yes, there are actually people who are allergic to water.  

Allergies can differ in how they affect a person. Seasonal allergies to pollen often cause watery eyes, runny noses, and difficulty breathing. 

Food allergy reactions often cause a person to vomit but can also involve a more dangerous drop in blood pressure or closing of the airways. 

And contact allergies to nickel or latex may cause a rash and itchy skin like eczema. 

While there’s really no way to prevent seasonal allergies, early introduction of peanut can actually help reduce your child’s risk of developing peanut allergies. Read more about early introduction and preventing food allergies in our Allergy Prevention series.

Keep learning about peanut allergy prevention with more information about babies and peanut allergies.