Everything you need to know about a tree nut allergy

Tree nuts provide the perfect parenting hack: You can sneak them into muffins, cookies and sauces and instantly boost the nutritional content of foods. But if your child is allergic to tree nuts, you face the challenge of keeping them away from the heart-healthy snacks that are becoming increasingly popular. Here’s what you need to know if your kid has a tree nut allergy.

What is a tree nut allergy, and how common is it?

A tree nut allergy develops when your body misidentifies a nut protein as dangerous and mounts an attack, releasing chemicals that cause an allergic reaction.

“Tree nut allergies are often quite severe,” says Harold Kim, an allergist in Kitchener, Ont., and president of the Canadian Society of Allergy and Clinical Immunology. In fact, tree nuts and peanuts are the leading cause of fatal anaphylaxis, accounting for up to 90 percent of deaths. Tree nuts alone cause 18 to 40 percent of anaphylactic reactions.

Most tree nut allergies are caused by nine nuts: walnuts, almonds, pistachios, cashews, pecans, hazelnuts, macadamia nuts, Brazil nuts and pine nuts. Tree nuts have hard shells and are different from peanuts, which are legumes.

Between one and two percent of children are allergic to tree nuts, and studies suggest that the rate is increasing as more parents reach for these protein-rich snacks for their kids. “I think we’re seeing more tree nut allergies because we’re eating more tree nuts in our society,” says Kim.

Food allergies, in general, are also increasing among children. No one knows exactly why, but there are a number of theories, including the hygiene hypothesis, that early exposure helps a child's immune system develop resistance, and the idea that highly allergenic foods have not been introduced early enough. “Our society is more allergic now, and as we get exposed to these foods, we’re more likely to respond to them with allergic reactions,” says Kim.

This is why parents are now urged to introduce tree nuts and other highly allergenic foods, such as peanuts and eggs, by six months of age to help reduce the chances of developing a food allergy.

What are the symptoms of a tree nut allergy?

The symptoms of a tree nut allergy range from mild itching to life-threatening anaphylaxis and typically set in soon after exposure. Many children experience skin reactions, such as hives and flushing. Other common symptoms include tightness in the throat, nausea, vomiting and diarrhea. The skin and respiratory, gastrointestinal and cardiovascular systems may all be involved.

Anaphylaxis is a life-threatening emergency that typically involves a rapid onset of symptoms from two or more body systems. The most serious symptoms of anaphylaxis are difficulty breathing and a drop in blood pressure, which may cause a child to become weak, groggy or dizzy and even pass out. On its own, a drop in blood pressure can suggest anaphylaxis.

Young children often have a hard time verbalizing their symptoms, so it’s important to know what to look for. Reactions can also be different every time. “Some parents say that their kids will grab at their tongues or throats,” says Kim, “while others say they become groggy.”

How do you treat a tree nut allergy? 

If your child has a mild reaction to a tree nut for the first time, such as itchy skin, Kim says it’s safe to stay home and watch them closely. If the reaction doesn’t progress, you should make an appointment with your doctor as soon as possible. If the reaction involves more than mild symptoms, you should call 911.

At the hospital, your child may be treated with epinephrine, a life-saving drug that stops the reaction. Other drugs, such as antihistamines and steroids, may also be given. If your child is diagnosed with a tree nut allergy, you should always have an epinephrine auto-injector (called by the brand name EpiPen or Allerject in Canada) on hand and make sure everyone who is caring for your child knows how to use it. At the first sign of a serious reaction, you should call 911 and give the child the autoinjector.

If your child has mild symptoms that are not progressing but are bothersome, such as itchy, watery eyes and hives, you can give them a non-drowsy antihistamine. Kim says it’s important to wait at least 30 minutes to ensure that the reaction isn’t escalating, as an antihistamine can mask the progression of symptoms.

Is there a cure for a tree nut allergy?

While there is no cure for a tree nut allergy, the good news is that oral immunotherapy, which involves consuming increasing doses of an allergen to build up tolerance, is at the experimental stage for tree nuts. “In the future, many of us will be doing oral immunotherapy for tree nuts, but we need some more science to make us feel comfortable doing that procedure,” says Kim.

How do you diagnose a tree nut allergy?

If you suspect that your child has a tree nut allergy, they should be seen by an allergist, who will likely do a skin prick test, a blood test or both. The skin prick test involves exposing skin to the suspected allergen and seeing how big of a weal (an area of irritated skin) develops around the site. The larger the area of irritated skin, the more likely it is that your child is allergic.

An oral food challenge, in which small amounts of the suspected allergen are consumed under the supervision of a doctor, may also be done. An oral food challenge is typically done if the child’s reaction and tests are not conclusive or to see if a child has developed tolerance to the allergen in the years following the initial diagnosis. Kim says an oral food challenge is typically only done if a child has less than a 50 percent chance of having a reaction.

When do tree nut allergies usually develop?

Tree nut allergies typically develop by age two, and a voluntary US allergy registry shows that 68 percent of children have reactions on their first known exposure. However, to become allergic to tree nuts, kids must first be exposed to them in some way. Experts are unsure of all the ways in which this could happen, but eating trace amounts or being exposed through broken skin (such as eczema) are possibilities.

Kim says it’s unlikely but possible that a baby could have a reaction to breastmilk with nut protein in it if the mother is consuming a lot of nuts. “The symptoms would be similar,” he says. “Sometimes infants are more likely to become lethargic.”

What foods should your child avoid if they have a tree nut allergy?

Studies have found that between 12 and 24 percent of people with tree nut allergies are allergic to more than one type of nut, and 20 to 68 percent are allergic to peanuts. Common allergies that occur together are pistachio and cashew, as well as walnut and pecan.

“We used to say that if you’re allergic to one nut, you should avoid all of them, but now we don’t do that,” says Kim. “If you’re not really allergic to something, you shouldn’t avoid it because you may become allergic to it later. Quality of life and nutrition are also reasons to keep some nuts in your diet.”

Tree nuts can be found in a variety of packaged foods (such as cereal, ice cream, candy and chips) and prepared foods (such as baked goods and restaurant dishes like pad thai and butter chicken). Tree nuts also show up in non-food products that kids can get their hands on, such as beanbags, soaps and pet foods.

In Canada, food labels must include the specific nuts that are found in products, and you should always ask about nuts at restaurants. Different tree nuts are often processed in the same facilities, so you need to be aware of the possibility of cross-contamination. However, precautionary labels that warn of potential cross-contamination are voluntary, so contact the company if you’re worried about a particular product.

Can a tree nut allergy be outgrown?

Tree nut allergies tend to be for life, and there is no "cure" but studies have found that about 10 percent of children outgrow them.

Parenting a kid with a tree nut allergy

Shahee Lakhani was at the grocery store checkout when she decided to get her 18-month-old son, Nurain, a bag of cashews to try for the first time. After paying, she broke off a quarter of a nut and gave it to him. Within seconds, he reacted. “It looked like he was gagging, so I put my finger in his mouth and yanked out all the pieces, but he still looked very uncomfortable,” recalls the Surrey, BC, mom.

On the drive home, she sat in the back seat with her son. “He was looking so limp and lifeless, I put my finger under his nose to see if he was breathing,” she says. “As soon as my husband parked the car outside the house, he threw up violently. When I took him inside to change him, he had violent diarrhea.”

Lakhani and her husband took Nurain to the hospital. When they arrived at the emergency department, the triage nurse said that he was experiencing anaphylaxis and rushed him in and gave him epinephrine. Nurain was diagnosed with a tree nut allergy, and his parents were told to keep him away from all nuts including peanuts—because he might have been allergic to those, too.

Nurain, who is now 15, has had several reactions over the years due to accidental exposure.“The moment his tongue gets itchy, he uses the EpiPen,” says Lakhani. “We don’t wait or question; we just call the ambulance and get to the hospital.” Lakhani adds that Nurain has laboured breathing and difficulty swallowing during a reaction.

In recent years, Nurain has done oral food challenges for walnut, almond and peanut and failed the walnut test and passed the other two. Based on the reactions he has had over the years, Lakhani says that he is definitely allergic to cashew, pistachio, walnut and pecan. She isn’t sure if he outgrew peanut and almond allergies or was never allergic to them in the first place.

Lakhani remains hopeful that Nurain will overcome his allergies but doesn’t let them get in the way of activities that the family enjoys, like going out to eat and travelling.

“We have a few ground rules that he has to abide by,” she says. “First of all, he can never, ever eat alone. He has to be with somebody who knows he has an allergy and knows how to use an EpiPen.”

Nurain also knows to read the labels on packaged foods and ask questions at restaurants, even if it’s something he has eaten before. Manufacturers can change their ingredients and restaurants can change their recipes, cautions Lakhani.

Lakhani has also become a skilled cupcake baker over the years, bringing dozens upon dozens of her own to various community events. “If there’s food involved, I’m the first one to say ‘I’ll bring it,’” she says. “My son can eat it if I know it’s safe, and nobody has to accommodate him.”

Read more: When your child’s food allergy leads to anxiety How to know if your kid has a food allergy or food intolerance