A peanut allergy is an immune system response to contact with peanut proteins. A peanut allergy response is usually caused by eating peanut, where it comes into contact with the mouth, saliva, and gut. But some peanut allergy responses can be from breathing in peanut dust or from skin contact (touching) peanut, peanut butter, or peanut dust.
Almost always, a peanut allergy is a reaction to one of 9 peanut proteins. This means that even people with a peanut allergy can usually eat highly-refined peanut oil, because it doesn’t have any peanut protein in it.
How Common Are Peanut Allergies?
Peanut allergies are very common. As recently as 2017, 5% of 1 year olds, or 1 in 20 babies, developed a peanut allergy. This may not seem like a lot, but considering 4 million babies are born in the U.S. every year, 5% is quite a large number.
The number of peanut allergies has been increasing. Between 2001 and 2017, the rate went from an estimated 1.7% to 5.2%. Because the rise is so recent, about 2.2% of children & teens in the U.S. have a peanut allergy.
The rate of peanut allergy is different worldwide. The United States, the United Kingdom, Canada, and Australia have the highest rates of peanut allergy, followed by France, Denmark and Israel. But peanut allergy is very low in Germany, and rare in Asian countries.
Components of Peanut Allergy
There are 9 major proteins in peanuts (latin name Arachis hypogaea, or Ara h). They are labeled Ara h 1 to 9. A person can be allergic to just one, or all 9 of the proteins. Which protein you are allergic to seems to predict what kind of allergic response you have to peanuts.
- Antibodies for Ara h 1 to 4 cause most of the peanut allergies as we know them
- IgE antibodies to Ara h 2 seems to predict anaphylaxis reactions to peanuts
- Antibodies to Ara h 5, 8, and 9 ONLY is associated with oral allergy syndrome instead of full peanut allergy
Testing for Peanut Allergy
If your baby has shown a reaction to peanuts, or if your baby has severe eczema or a milk allergy, your doctor may want to test for a peanut allergy.
In studies of skin prick testing, a wheal of ≥8 mm in size correctly predicted peanut allergy over 95% of the time in children and adults. In children under 2, a wheal of ≥4 mm predicted 100% of peanut allergy. If a wheal size is smaller than these thresholds, blood testing or an oral food challenge may make sense.
Blood, or specific IgE testing, for peanut allergy will test for peanut overall, as well as each of the 9 proteins in peanut. This will help a doctor decide if an oral food challenge makes sense for your baby. An oral food challenge is the only true test of a peanut allergy.
What a Peanut Allergy Can Mean
Between 25% and 50% of babies with peanut allergy develop a tree nut allergy as well. Peanut-specific IgE antibodies have been shown to react with pecan/walnut, almond, Brazil nut, and hazelnut. This is likely why the chance of those allergies increases after someone already has a peanut allergy.
Babies with peanut allergy also seem to have a high chance of non-nut allergies. Egg is the most common (~50%), followed by cow's milk (~25%), fish (~10%), shellfish (~10%), soy (7%), wheat (6%), and sesame seed (6%).
Strangely enough, less than 5 to 10 percent of children with peanut allergy also become allergic to other legumes like soy, peas, and green beans, even though they are all legumes!
Lastly, peanut allergy seems to be a marker of widespread allergic disease. Remember all allergic diseases are linked, and some might argue, the same disease. Many children with peanut allergy often have asthma (60% to 75%), atopic dermatitis (60% to 75%), and/or allergic rhinitis (55% to 60%).
Having asthma increases the risk for an anaphylactic reaction to peanut.
What is Wrong with Peanuts?
No one knows exactly why so many people started becoming allergic to peanuts. There are weird theories like “peanut-protein is similar to proteins in dangerous worms.” And there are disproven theories like “people made vaccines with peanut” (vaccines are not made with peanuts).
Some proposed explanations are that:
- Proteins in peanuts, tree nuts, and seeds are super stable, so if they are left on surfaces, they will stick around and get into cracked eczema skin. We know peanut allergy is way more likely and persistent in kids who had skin infections when they were little.
- Ara h 1 in heated peanuts triggers the body to make more antibodies. Almost no other foods do this.
- Nuts are often served with oils, which also seems to trigger a bigger immune response
Peanut Allergies May Be Prevented
No matter what, you can take steps to keep your baby as safe as possible.