Cross-Reactivity and Food Allergies

A food allergy can be complex and sometimes life-threatening. People with known allergies can usually avoid foods that contain their allergens, but many may not know about food allergy cross-reactivity and the surprise allergic reactions they can cause. 

Let’s discover what cross-reactive food allergies are, how they may affect the foods you can eat, and how you can determine which foods to avoid.

What Is Allergy Cross-Reactivity?

A cross-reactive allergic reaction happens when one or more substances have similar proteins. These protein similarities typically exist between pollen and food substances. If you are allergic to grass pollen, you may also experience an allergic reaction when eating melons, tomatoes, or oranges. This means that a protein in grass pollen can be similar to a protein in tomatoes, causing you to have an allergic reaction to both and resulting in a cross-reactive allergy.

What Is Pollen Food Allergy Syndrome?

The allergic reaction caused by cross-reactivity is called Pollen Food Allergy Syndrome (PFAS). If you eat a food that shares protein properties with pollen you are allergic to, you may feel an allergic reaction in your lips, tongue, throat, or the inside of your cheeks. 

PFAS is also known as Oral Allergy Syndrome (OAS) and can present as: 

  • Itchy throat 
  • Tingling or scratchy mouth or lips 
  • Swelling of the throat, lips, or tongue

Common Instances of Allergy Cross-Reactivity

Mammal Milk

If a person is allergic to the proteins in cows’ milk, they are likely to have cross allergies with milk from other mammals, including sheep, goats, deer, buffalo, and more.

Animal Food Groups

It seems reasonable that if a person is allergic to the proteins in cows’ milk, they would also be allergic to other cow byproducts. However, this is typically not the case. You could be allergic to the protein in eggs but have no issues with chicken.

Peanuts and Other Legumes

A common concern for people with a peanut allergy is that they are also allergic to other beans in the legume family, like soybeans, lentils, and other beans. While it is likely that an individual may test positive for a cross-reactivity allergy to other legumes, most people can still eat them without a problem. You should work with your physician to determine if you can eat other legumes with a peanut allergy.

Peanuts and Tree Nuts

Peanuts are not part of the same family as tree nuts like walnuts, almonds, and cashews. However, many children with a peanut allergy also develop a cross-reactivity food allergy to tree nuts.


Studies show that if a person is allergic to one type of fish, they are more likely to have cross-reactivity allergies to other types of fish.


Just as fish have high cross-reactivity issues, so do shellfish. If you are allergic to shrimp, your chance of having cross-reactivity allergies to lobster, crab, or crawfish increases significantly.

What Is Cross-Contact?

Cross-contact, which is different from cross-reactivity, happens when an ingredient contaminates a food it wasn’t meant to touch. An example of cross-contact would be peanut-free food products made in the same facility as products containing peanuts. There is the possibility that the non-peanut products can be contaminated by the peanut products, creating a potential allergy risk.

Determine Cross-Reactivity Allergies With Immuno Labs

At Immuno Labs, we offer specialized sensitivity testing to help you discover your food sensitivities as well as cross-reactivity allergies. Work with us to determine which foods are safe to eat and which foods you should avoid.