A tree nut allergy is one of the most common food allergies in both adults and children. Tree nuts include almonds, Brazil nuts, cashews, macadamia nuts, pistachios, walnuts, pecans, walnuts, hazel nuts (and pine nuts in the US). Tree nut and peanut allergies are responsible for the most severe food related allergic reactions, including life-threatening (anaphylactic) or even fatal reactions.
Allergies to walnuts are unpredictable and potentially severe, with symptoms usually beginning at a young age. In this article, we explain where walnuts are found, cross-reactivity versus co-reactivity, the link to pollen allergies, symptoms of an allergic reaction, testing, diagnosis and management.
Walnuts are typically found within the shells of walnut trees’ fruit, known as walnuts or walnut kernels. They are commonly used in cooking and baking, and they can be added to various dishes, salads, desserts including ice creams, snacks and flavoured coffees. Walnuts are also used to produce tree nut oils, which is used for culinary and cosmetic purposes including hair care products.
Cross-reactivity versus Co-reactivity
Cross-reactivity and co-reactivity is an essential concept to understand when dealing with nut allergies. Individuals with allergies to peanuts and tree nuts frequently experience reactions stemming from various nut types; sometimes these are due to related allergens (such as walnut and pecan nut – known as cross-reactivity), but they can also react to nuts that do not originating from closely related plant species (such as walnut, hazelnut and macadamia nut allergy known as co-reactivity).
Primary Versus Secondary Allergy to Walnuts
In primary walnut allergy, the allergic reaction is triggered by IgE antibodies directed against proteins present in walnuts that withstand processes like heat and digestion. This type of walnut allergy is responsible for the more severe reactions, including life-threatening (anaphylactic) reactions. In children with this type of primary walnut allergy, they often require adrenaline epinephrine auto injectors as part of their food allergy treatment plan as well as antihistamines.
In secondary walnut allergy, the allergic reaction is triggered by IgE antibodies directed against proteins present in walnuts that are broken down by processes like heat and digestion. This can be observed in individuals with hay fever due to tree pollen allergies. This scenario can occur when an individual initially exhibits an allergy to tree pollen, subsequently developing reactions to tree nuts. This phenomenon arises due to cross-reactivity, wherein proteins present in pollen share similarities with proteins in tree nuts.
This type of walnut allergy is responsible for milder reactions, primarily affecting the mouth and giving rise to pollen food syndrome also known as “oral allergy syndrome” (OAS). In children with this type of primary walnut allergy, they often require only antihistamines for their food allergy treatment plan.
Symptoms of Primary Walnut Allergy
Possible reactions, from least severe to most severe, can include:
- Itching sensation in the mouth, throat, eyes, ears, skin, or other regions
- Hives – local or generalised
- Swelling in the lips, tongue, or face, also known as angioedema
- Difficulty swallowing or hoarse voice
- Sneezing, nasal congestion or a runny nose
- Sensations of nausea, abdominal discomfort, vomiting, or diarrhoea
- Wheezing or coughing
- Going pale, floppy or lethargic
It’s important to note that reactions to allergies can vary from person to person, and symptoms can range from mild to severe. If you suspect a walnut allergy, it’s crucial to consult with a healthcare professional for proper diagnosis and guidance.
Symptoms of Secondary Walnut Allergy
Reactions are usually milder and localised to the mouth or face:
- Itching sensation in the mouth, tongue or ears
- Itchy throat and tickly cough
- Localised hives around the mouth
- Mild swelling in the lips
- Sensations of nausea, abdominal discomfort, vomiting
Diagnosis and Testing
If you suspect your child might have a walnut allergy, it’s crucial to consult a doctor for proper allergy diagnosis and food allergy management. Skin prick tests are a common method used to determine whether a child is allergic to walnuts. During this test, tiny amounts of standard extracts of the walnut allergen and fresh walnut are placed on the skin and any local wheal (bump) is measured.
This helps the doctor identify the likelihood of whether your child is allergic to walnuts, but not the severity of reaction. To differentiate between primary and secondary food allergy, an allergy blood test can measure the proteins inside walnut that your child is allergic to to confirm whether your child has primary or secondary walnut allergy (or a mixture of both).
The gold standard of testing is the oral food challenge, which can be performed if there is uncertainty with the diagnosis or if the skin or blood tests indicate that your child has grown out of their walnut allergy. At Children’s Allergy Doctors, we can arrange an oral food challenge or supervised feed (in clinic) to confirm whether your child is allergic or tolerant to walnut.
Managing Walnut Allergy
Upon receiving a diagnosis of walnut allergy for your child, there are several precautions you can implement to ensure their well-being. Firstly, avoid eating walnuts and products containing forms of walnut.
Check food labelling carefully, as walnuts might be present in unexpected places. Following the introduction of Natasha’s Law, food businesses are now required to include full ingredients on pre-packed for direct sake foods. Reactions to nuts might also emerge due to concealed nut components or minute traces of nuts and specific seeds unintentionally incorporated during food processing or production.
Exercise vigilance when eating at restaurants and make sure to communicate your child’s allergy to the restaurant personnel. This step is crucial to avoid cross-contact (previously known as cross-contamination), where remnants of the allergen might be present in the food due to the sharing of utensils or food preparation areas.
It is commonly recommended in patients allergic to any tree nut to avoid all tree nuts; however, children with one nut allergy may go on to develop more nut allergies if this approach is taken. At Children’s Allergy Doctors, we recommend finding out which nut your child is allergic to and then introducing other nuts to prevent the development of further nut allergies.
Oral Immunotherapy for Walnut
At Children’s Allergy Doctors, we are proud to offer Food Oral Immunotherapy (OIT) also known as Food Allergy Desensitisation, Oral Desensitisation (OD) or Food Desensitisation to walnut.
This is a process where you gradually introduce increasing amounts of the walnut into the child’s diet under supervision, to reduce the risk of allergic symptoms to accidental exposure to walnut and reduce severity of reactions, thereby reducing social restrictions and improving quality of life.
At Children’s Allergy Doctors, we offer this only in preschool children. The process takes 4-14 months depending on the walnut protocol your child is allocated to (which is personalised to their risk of reaction).
How can Children’s Allergy Doctors help?
Here at Children’s Allergy Doctors we provide a full range services for all allergy conditions. We aim to be with you every step of the way, from allergy diagnosis through to helping you with food allergy management and treatment.
Walnut allergies, like other food allergies, can be concerning for parents. Understanding the potential allergic reactions, cross-reactivity, and testing methods is essential for managing your child’s health effectively. With proper precautions and awareness, your child can lead a healthy and happy life, even with allergies.
If you would like to find out more about walnut allergy or any other aspect of children’s allergies, please contact our practice team on 0203 146 7721 or email firstname.lastname@example.org.