The LEAP Study: Learning Early About Peanut Allergy

 In Allergies, Food Allergy Awareness, Peanut Allergy, Treating Food Allergies

The LEAP Study: (Learning Early About Peanut Allergy). How was it done?

The LEAP study is an outstanding example of the application of careful science to a problem that impacts millions. The study was designed to answer the question: Can early (before one year of age) introduction of peanut decrease the risk of developing peanut allergy? The answer is yes!

In order to make good use of the lessons learned in the LEAP study, it’s important to understand why and how the study was done. It has become increasingly clear over the past ten years that the most likely cause of food allergy is contact exposure through the skin. We know that it is impossible to have an allergic reaction the first time you come in contact with a food, and yet, more than 90% of peanut allergy reactions in infants and toddlers occur with the first known exposure. That means that these youngsters have had some contact with peanuts that nobody was aware of.

We also know that children with eczema (injured skin) have an increased risk of developing food allergy. It is likely that the first exposure that leads to peanut allergy is a trace contact from someone who was eating peanuts or peanut butter and then held the child. There have been reports over the past several years that early exposure to foods decreases the risk of allergy to those foods. The idea is that eating a food usually results in tolerance, but when the first exposure is through the skin, food allergy often results.

The LEAP study enrolled over 600 children, ages four to <11 months, who were thought to be at increased risk for developing peanut allergy because they had severe eczema, egg allergy or both. Family history of food allergy was not taken into consideration. Children who were eating peanut products, who were suspected to have peanut allergy or who had a positive peanut skin test were excluded.

The infants were given a peanut product three times a week until five years of age or just followed the traditional avoidance management strategy. Children were monitored during the course of the study and, when they reached five years of age were retested and challenged in a controlled medical setting.

The LEAP Study: (Learning Early About Peanut Allergy) Study. What was learned?

Although peanut skin testing and blood testing are very helpful in understanding the risk of peanut allergy, the only way to really know if there is peanut allergy or not is a peanut challenge. In a peanut challenge, tiny but increasing amounts of peanut are given until the target dose is reached. In the study, the target dose for the enrolling infants was equal to about four peanuts. At the end of the five-year treatment, the target dose was equal to about eight peanuts.

The primary result was to show that children who ate peanuts (equal to about four peanuts) three times a week until age five were significantly less likely to develop peanut allergy than the children who followed the avoidance management strategy. Some children developed peanut allergy despite routine exposure to peanut.

Other important findings show that most, but not all, infants with a very low or negative peanut skin test are not allergic. The only way to know for sure is a peanut challenge. Children with a moderately positive peanut skin test are more likely to be peanut allergic and more likely to develop peanut allergy in the future. Children with strongly positive peanut skin tests were excluded from the study.

What was NOT learned from the LEAP Study?

Although very valuable, the LEAP Study only answered the questions it asked. Among the important but unanswered questions are:

  • Will early peanut introduction make a difference for children with mild eczema? What about children with no eczema and no other risk factors for peanut allergy?
  • Will early peanut introduction make a difference for milk allergic children? What about allergy to other foods?
  • Is it necessary to eat peanut three times a week or would twice a week work as well? Would four or five times a week work better?
  • Is it necessary to eat peanut for four to five years or would two or three years be enough?
  • Will allergy to other foods (milk, egg, nuts) respond to the approach used in the LEAP study?

Should we do anything differently now that we have the information from the LEAP Study?

There are strong recommendations based on the results of the LEAP Study:

  • Children, under one year of age, at increased risk for peanut allergy because of severe eczema or food allergy should be skin tested to peanut.
  • If the skin test is negative or mildly or moderately positive, consider a peanut challenge in a controlled medical setting.
  • If the infant passes the peanut challenge, they should eat the equivalent of four peanuts at least three days a week until at least age five.

Recommendations to consider based on extended interpretations of the results of the LEAP Study:

  • Apply the LEAP approach with peanuts to infants with allergy to other foods, mild eczema, other allergic diseases such as chronic wheezing, or a family history of food allergy.
  • Apply the LEAP approach using milk or egg in children at increased risk of developing allergy to milk or egg.
  • Apply the LEAP approach when there are weakly positive in vitro (Immunocap) food allergy test results in a child who has not had a reaction to that food.


  • Because even a child with a negative skin test, but with severe eczema or egg allergy may react to peanut, first exposure to peanut should always be supervised by a physician experienced in performing food challenges.
  • “Testing” for peanut allergy by applying peanut butter to the skin of an infant is not reliable, but may, in fact, cause peanut allergy.
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