Updated September 01, 2015.

What is Peanut Allergy?

Peanut, scientific name Arachis hypogeal, is a legume that is a common cause of food allergies. Peanut allergy is known to potentially be very dangerous and even life-threatening, particularly in adolescents and young adults, as well as in people with asthma.

How Common is Peanut Allergy?

Peanut allergy is the most common form of food allergy in school age children and adults.

Milk and egg allergy are more common in infants and toddlers, but allergies to these foods are commonly outgrown by school age. Recent studies show that in North America and the United Kingdom, 1% of children have peanut allergy.
It is possible for adults (who were not allergic as children) to develop a new allergy to peanut. In these cases, peanut allergy tends to be less severe, and is likely caused by the oral allergy syndrome as a result of birch allergy.

Peanut allergy is much less common in other parts of the world compared to Westernized countries. Despite peanut being a major food source in Asia, peanut allergy is uncommon. This is thought to be due to the common method of cooking peanuts in Asia, frying and boiling, which makes the food less allergenic. Dry roasting, the common method of cooking peanuts in the United States, has been shown to make peanuts more allergenic.

Why Is Peanut Allergy Becoming More Common?

The occurrence of peanut allergy has doubled in the past 10 to 20 years, and the reason for this increase is not completely clear.

Possibilities for this increase include topical exposure to peanut proteins in skin creams containing peanut oil, exposure to peanut proteins in breast milk or during pregnancy, as well as exposure to cross-reacting (similar) foods, such as soy. At the present time, it is not known why peanut allergy is becoming more common.

How is Peanut Allergy Diagnosed?

Peanut allergy is diagnosed in much the same as other food allergies. When symptoms consistent with food allergies occur after eating peanut-containing foods, an allergist will perform allergy testing. A positive allergy test, along with a history of a person experiencing symptoms with eating peanuts, makes a diagnosis of peanut allergy.

How Often Does a Person Outgrow Peanut Allergy?

Only about 20% of children will outgrow peanut allergy by the time they reach school age. For many people, peanut allergy may be a lifelong disease. Those people who outgrow their peanut allergy typically have milder reactions, smaller skin test reactions, and fewer allergies in general.
Physicians can predict resolution of peanut allergy with the use of RAST to peanut. A RAST level of less than 5 kU/L (kiliunits per liter) is suggestive of outgrowing peanut allergy, and that a person may pass an oral food challenge to peanut. Some people who have passed an oral food challenge to peanut have become re-allergic to peanuts if they don’t eat peanuts enough after they have outgrown peanut allergy. For this reason, a person who has outgrown peanut allergy should continue to have injectable epinephrine available for emergency use.

Is it Common to Accidentally Eat Peanuts?

Because peanuts are such a common food in Westernized diets, accidental exposure to peanuts is common. Peanut-allergic people accidentally eat peanuts every 3-5 years, and a recent study of Canadian peanut-allergic children showed that nearly 15% accidentally ate peanuts over a one-year period of time.

What Other Foods Should Be Avoided?

Peanuts belong to the legume family, which also includes beans, peas and soy. While it is common for a person allergic to peanut to have positive allergy tests to other legumes, allergic reactions from eating these other legumes occurs in only 5% of people.
Lupine is another legume commonly ground into flour and used for various baking purposes. Unlike other legumes, people with peanut allergy can frequently experience allergic reactions to lupine, and therefore this food should be avoided.

People with peanut allergy may also be allergic to treenuts, such as almonds, cashews, walnuts and pecans. In fact, a recent study showed that about 1 in every 3 people (33%) with peanut allergy is also allergic to at least one treenut. For this reason, as well as the fact that cross-contamination among treenuts and peanuts is common (for instance, where you find one, you tend to find the other), I typically recommend that people with peanut allergy avoid eating all nuts.

You've only read half the story! Don't miss out on page 2: Treatment of Peanut Allergies